East Otter Tail County Water Quality Factsheet
Rush Lake
Vitals
MN Lake ID:
Zoning Authority:
Lake Classification:
Major Drainage Basin:
Latitude/Longitude:
Water Body Type:
Invasive Species:
DNR ID: 56-0141-00
56-0141-00
Ottertail
Drainage Lake
Red River
46.49027778/-95.53083333
Public
None
Total Phosphorus
Rush Lake is phosphorus limited, which means that algae
and aquatic plant growth is dependent upon available
phosphorus. Total phosphorus was evaluated in Rush Lake
in 1978, 1979, and 1996-2011. Most of the spring and late
summer/fall readings fall within the eutrophic range.
Midsummer samples fall into the mesotrophic range. Spring
runoff and lake turnover could explain the spikes in early
and late season results. The increase in phosphorus at the
end of the summer could indicate internal loading. Total
phosphorus does not have a trend.
Physical Characteristics
Surface area (acres):
Littoral area (acres):
% Littoral area:
Max depth (ft):
Mean depth (ft):
Inlets/Outlets/Accesses:
Lakeshed to lake area ratio:
5,234
3,511
67%
65
12
5/1/2
2:1
Chlorophyll a
Chlorophyll a is the pigment that makes plants and algae
green. It is tested in lakes to determine the algae
Rush Lake total phosphorus, chlorophyll a, and transparency historical ranges.
The arrow represents the range and the black dot represents the historical mean
concentration or how green the water is. Chlorophyll a
(Primary Site 206). Figure adapted after Moore and Thornton, [Ed.]. 1988. Lake
concentrations greater than 10 ug/L are perceived as a mild
and Reservoir Restoration Guidance Manual. (Doc. No. EPA 440/5-88-002)
algae bloom, while concentrations greater than 20 ug/L are
perceived as a nuisance. Chlorophyll a was evaluated in
Rush Lake in 1978, 1979, and 1996-2011. Concentrations
varied throughout the season, but were consistently greater than 10 ug/L, with nuisance algae blooms (greater than 20 ug/L)
occurring in August and September. This is typical of a eutrophic lake. Chlorophyll a concentrations had no trend.
Transparency (Secchi Depth)
Transparency is how easily light can pass through a substance. In lakes it is how deep sunlight
penetrates through the water. Plants and algae need sunlight to grow, therefore they are only
found in areas of lakes where the sun penetrates. Water transparency depends on the amount of
particles in the water. An increase in particulates results in a decrease in
Rush Lake
transparency. The annual mean transparency for Rush Lake ranges from 4.3 to 8.9
feet. The lake has a data set extending back to the 1970s, which is rare and very
helpful when looking at long-term water quality. The transparency throughout the
lake appears to fluctuate over the years, with the best annual transparency seen in 1996 at site 204.
There is no transparency trend.
100
Hypereutrophic
70
Eutrophic
50
Mesotrophic
40
Oligotrophic
Trophic State Index (TSI)
Phosphorus (nutrients), chlorophyll a (algae concentration), and Secchi depth (transparency) are
interrelated. As phosphorus increases, there is more food available for algae, resulting in increased
0
algal concentrations. When algal concentrations increase, the water becomes less transparent and
the Secchi depth decreases. The results from these three measurements cover different units and ranges and thus cannot be
directly compared or averaged. In order to standardize these measurements to make them directly comparable, we convert them
to a tropic state index (TSI). The mean TSI for Rush Lake is 52; falling into the eutrophic range (TSI 50-70). These lakes
characteristically have greenwater most of the summer. “Eu” means true, and the root “tropy” means nutrients, therefore,
eutrophic literally means truly nutrient rich (phosphorus). Eutrophic lakes are usually shallow with abundant aquatic plants and
algae, and are found near fertile soils.
Local association information: The Rush Lake Association
Rush Lake
56-0141-00 OTTER TAIL COUNTY
Lake Water Quality
Summary
Rush Lake is located two miles north of Ottertail, MN in Otter Tail
County. It covers 5,234 acres and has a rounded shape.
Rush Lake has five inlets and one outlet, which classify it as a
drainage lake (Figure 1). The main inlet is located near the
middle of the north shore, where the Otter Tail River flows into
the lake. The two inlets along the western tip of Rush Lake drain
small areas to the west. A fourth inlet enters along the south
shore and a fifth drains from Boedigheimer Lake. The Otter Tail
River outlets to the west and flows into the lake.
Water quality data have been collected on Rush Lake since 1956 (Tables 2-3). These data show that
the lake is eutrophic, a characteristic of shallow lakes with abundant aquatic plants, algae, and bass
fisheries (see page 9).
The Rush Lake Association is a group consisting of property owners on and near Rush Lake
concerned about future enjoyment of the lake. They raise money for fish stocking, monitor water
quality, and are members of the Otter Tail County Coalition of Lake Associations COLA.
Table 1. Rush Lake location and key physical characteristics.
Location Data
Physical Characteristics
56-0141-00
Surface area (acres):
5234
County:
Otter Tail
Littoral area (acres):
3511
Northern Central Hardwood
Forests
% Littoral area:
67%
Ecoregion:
Max depth (ft), (m):
65, 20
Major Drainage Basin:
Red River
Inlets:
5
Latitude/Longitude:
46.49027778 / -95.53083333
Outlets:
1
Invasive Species:
None
Public Accesses:
2
MN Lake ID:
Table 2. Availability of primary data types for Rush Lake.
Data Availability
Transparency data
Excellent set of data with historical records and
continuous data from 1997–2011.
Chemical data
Excellent set of data with continuous chlorophyll a
and total phosphorus data from 1997–2011.
Inlet/Outlet data
Good data set from two inlets along the Otter Tail
River.
Recommendations
For recommendations refer to page 19.
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Lake Map
Figure 1. Map of Rush Lake with 2010 aerial imagery and illustrations of lake depth contour lines, sample site
locations, inlets and outlets, and public access points. The light green areas in the lake illustrate the littoral
zone, where the sunlight can usually reach the lake bottom allowing aquatic plants to grow.
Table 3. Monitoring programs and associated monitoring sites.
Lake Site
Depth (ft)
Monitoring Programs
100
102
103
201
202
203
204
205* Primary Site
206
30
30
40
17
17
20
15
60
32
MPCA: 1956, 1971
MPCA: 1978, 1979, 1998
MPCA: 1985, 1998
CLMP: 1973–1975
CLMP: 1973–1975
CLMP: 1981–1984
CLMP: 1985–1991, 1993–1995
MPCA: 1978, 1979, 1998; CLMP: 1996, 1999; RMBEL: 1996–2011
CLMP: 1996
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Average Water Quality Statistics
The information below describes available chemical data for the primary site (205) of Rush Lake
through 2011. The data set is limited, and all parameters, with the exception of total phosphorus,
chlorophyll a, and Secchi depth, are means for the MPCA Lake Monitoring Program from 1979 and
1998.
Minnesota is divided into 7 ecoregions based on land use, vegetation, precipitation, and geology. The
MPCA has developed a way to determine the average range of water quality expected for lakes in
each ecoregion. For more information, see page 10.
Table 4. Water quality means compared to ecoregion ranges and impaired waters standard.
Impaired
Waters
Standard2
Parameter
Mean
Ecoregion
Range1
Total phosphorus (ug/L)
28
23–50
> 40
3
12
5–22
> 14
Chlorophyll a max (ug/L)
27
7–37
Secchi depth (ft)
6.7
4.9–10.5
Dissolved oxygen
Polymitic
Chlorophyll a (ug/L)
Interpretation
Results are within the expected
range for the Ecoregion.
<7
Dissolved oxygen depth profiles
mix periodically through the
summer.
(see page 9)
0.8
< 0.6–1.2
Indicates insufficient nitrogen to
support summer nitrogen-induced
algae blooms.
Alkalinity (mg/L)
151
75–150
Indicates a low sensitivity to acid
rain and a good buffering capacity.
Color (Pt-Co Units)
18
10–20
Indicates moderately clear water
with little to no tannins (brown
stain).
pH
8.4
8.6–8.8
Within the expected range for the
ecoregion. Lake water pH less
than 6.5 can affect fish spawning
and the solubility of metals in the
water.
Chloride (mg/L)
4.5
4–10
Within the expected range for the
ecoregion.
Total Suspended Solids
6
2–6
Indicates low suspended solids
and clear water.
315
300–400
Within the expected range for the
ecoregion.
31:1
25:1–35:1
Indicates the lake is phosphorus
limited, which means that algae
growth is limited by the amount of
phosphorus in the lake.
Total Kjeldahl Nitrogen
(mg/L)
(mg/L)
Specific Conductance
(umhos/cm)
Total Nitrogen :Total
Phosphorus
1
The ecoregion range is the 25th–75th percentile of summer means from ecoregion reference lakes
For further information regarding the Impaired Waters Assessment program, refer to http://www.pca.state.mn.us/water/tmdl/index.html
3
Chlorophyll a measurements have been corrected for pheophytin
Units: 1 mg/L (ppm) = 1,000 ug/L (ppb)
2
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Water Quality Characteristics - Historical Means and Ranges
Table 5. Water quality means and ranges for primary sites.
Parameters
Total Phosphorus Mean (ug/L):
Total Phosphorus Min:
Total Phosphorus Max:
Number of Observations:
Chlorophyll a Mean (ug/L):
Chlorophyll a Min:
Chlorophyll a Max:
Number of Observations:
Secchi Depth Mean (ft):
Secchi Depth Min:
Secchi Depth Max:
Number of Observations:
Primary
Site
205
Site
203
Site
204
28
14
45
97
12
1
27
94
6.6
3.5
12.0
94
6.6
4.0
15.0
69
6.6
3.0
12.0
67
Figure 2. Rush Lake total phosphorus, chlorophyll a, and transparency historical ranges. The arrow
represents the range and the black dot represents the historical mean (Primary Site 205). Figure adapted
after Moore and Thornton, [Ed.]. 1988. Lake and Reservoir Restoration Guidance Manual. (Doc. No. EPA 440/5-88-002)
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Transparency (Secchi Depth)
Transparency is how easily light can pass through a substance. In lakes it is how deep sunlight
penetrates through the water. Plants and algae need sunlight to grow, so they are only found in areas
of lakes where the sun penetrates. Water transparency depends on the amount of particles in the
water. An increase in particulates results in a decrease in transparency. The transparency varies
year to year due to changes in weather, precipitation, lake use, flooding, temperature, lake levels, etc.
The annual mean transparency for Rush Lake ranges from 4.3 to 8.9 feet. The lake has a data set
extending back to the 1970s, which is rare and very helpful when looking at long-term water quality.
The transparency throughout the lake appears fluctuate over years, with the best annual transparency
was seen in 1996 at site 204. Visibility dipped in 1987–1989, 2005, and 2006.
Transparency monitoring should be continued annually at site 205 in order to track water quality
changes.
10
Transparency: Annual Means
9
Secchi Depth (ft)
8
7
6
5
4
Site 201
3
Site 202
2
Site 203
Site 204
1
Site 205
0
Figure 3. Annual mean transparency compared to long-term mean transparency.
Rush Lake transparency ranges from 3.5 to 12.0 ft at the primary site (205). Figure 4 shows the
seasonal transparency dynamics. High in May and June, the transparency declines through August.
If monitoring continued into early October, it would most likely have a more pronounced rebound after
fall turnover. This transparency dynamic is typical of a northern Minnesota lake. The dynamics have
to do with algae and zooplankton population dynamics, and lake turnover.
It is important for lake residents to understand the seasonal transparency dynamics in their lake so
they are not concerned as to why it is lower in August than June. It is typical for a lake to vary
throughout the summer.
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Transparency: Annual Means
14.0
12.0
Secchi Depth (ft)
10.0
8.0
6.0
4.0
2.0
0.0
1978
1979
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Poly. (Pattern)
Figure 4. Seasonal transparency dynamics and year to year comparison (Primary Site 205). The black line
represents the seasonal pattern of the data.
User Perceptions
When volunteers collect Secchi depth readings, they record their observations of the water based on
the physical appearance and the recreational suitability. These perceptions can be compared to
water quality parameters to see how the lake user would experience the lake at that time. Looking at
transparency data, as the Secchi depth decreases the perception of the lake's physical appearance
rating decreases. Rush Lake was rated as being not quite crystal clear 74% of the time between
1996, 1998, 1999, and 2008–2011 (site 205).
10%
Physical Appearance Rating
16%
16%
Crystal clear water
74%
Not quite crystal clear – a little algae visible
10%
Definite algae – green, yellow, or brown color
apparent
0%
High algae levels with limited clarity and/or mild
odor apparent
0%
Severely high algae levels
74%
Figure 5. Physical appearance rating, as rated by the volunteer monitor (1996,
1998, 1999, 2008–2011 (site 205).
As the Secchi depth decreases, the perception of recreational suitability of the lake decreases. Rush
Lake was rated as being beautiful 35% of the time from 1996, 1998, 1999, and 2008–2011 (site 205).
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Recreational Suitability Rating
3%
13%
35%
35%
Beautiful, could not be better
39%
Very minor aesthetic problems; excellent for
swimming, boating
10%
Swimming and aesthetic enjoyment of the lake
slightly impaired because of algae levels
13%
Desire to swim and level of enjoyment of the lake
substantially reduced because of algae levels
3%
Swimming and aesthetic enjoyment of the lake
nearly impossible because of algae levels
10%
39%
Figure 6. Recreational suitability rating, as rated by the volunteer monitor from 1996, 1998,
1999, and 2008–2011 (site 205).
Total Phosphorus
Total Phosphorous
50
45
Total Phosporous ug/L
Rush Lake is
phosphorus limited,
which means that
algae and aquatic
plant growth is
dependent upon
available phosphorus.
40
35
Eutrophic
30
Total phosphorus was
25
evaluated in Rush
Lake in 1978, 1979,
20
and 1996–2011. Most
15
Mesotrophic
of the spring and late
summer/fall samples
10
are within the
Oligotrophic
5
eutrophic range and
the mid-summer
0
samples are in the
mesotrophic range.
Spring run-off and lake
turn-over could explain
Figure 7. Historical total phosphorus concentrations (ug/L) for Rush Lake.
the spikes in early and
late season results.
The increase in
phosphorus at the end of the summer could indicate internal loading.
1978
1979
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Phosphorus should continue to be monitored to track any future changes in water quality.
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Chlorophyll a
Concentrations greater
than 10 ug/L are perceived
as a mild algae bloom,
while concentrations
greater than 20 ug/L are
perceived as a nuisance.
Chlorophyll a
30
25
Chlorophyll a ug/L
Chlorophyll a is the pigment
that makes plants and
algae green. It is tested in
lakes to determine the
algae concentration or how
green the water is.
20
15
10
5
1978
1979
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Minor Algae
Nuisance Algae
Chlorophyll a was
0
evaluated in Rush Lake in
1978, 1979, and 1996–
Figure 8. Chlorophyll a concentrations (ug/L) for Rush Lake.
2011 (site 205).
Concentrations were found
to vary throughout each season, consistently greater than 10 ug/L, with nuisance algae blooms
(greater than 20 ug/L) occur in August and September. These results are consistent with the
transparency and total phosphorus results in that water quality declines over the course of the
summer. This is typical for a eutrophic lake.
Dissolved Oxygen
Dissolved Oxygen (DO) is the amount of oxygen dissolved in
lake water. Oxygen is necessary for all living organisms to
survive except for some bacteria. Living organisms breathe in
oxygen that is dissolved in the water. Dissolved oxygen levels
of <5 mg/L are typically avoided by game fisheries.
Rush Lake is a relatively shallow lake, with a few deep holes
reaching a maximum depth of 65 ft. Dissolved oxygen profiles
from 1978, 1979, and 1998 indicate that sites 102 and 205
weakly stratify. With a large surface area, much of the lake is
less than 15 feet deep; periods of windy weather can cause the
lake profile to mix. Benthic phosphorus samples taken in 1978
and 1979 indicate minor internal loading (10–50 ug/L). For
much of the summer dissolved oxygen levels remain above 5
mg/L, with game fish species present down to 40–50 feet.
Figure 9. Dissolved oxygen profile for Rush Lake
in 1998 at site 205.
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Trophic State Index
Table 6. Trophic State Index for Rush Lake.
Phosphorus (nutrients), chlorophyll a (algae
concentration), and Secchi depth
(transparency) are related. As phosphorus
increases, there is more food available for
algae, resulting in increased algal
concentrations. When algal concentrations
increase, the water becomes less transparent
and the Secchi depth decreases.
Trophic State Index
Site 205
Site 204
TSI Total Phosphorus 52
-TSI Chlorophyll a
55
-TSI Secchi
50
50
TSI Mean
52
Eutrophic
Trophic State:
Numbers represent the mean TSI for each parameter.
The results from these three measurements
cover different units and ranges and thus cannot be
directly compared to each other or averaged. In order to
standardize these three measurements to make them
directly comparable, we convert them to a trophic state
index (TSI).
The mean TSI for Rush Lake (site 205)
shows that the lake is eutrophic. There is
Rush Lake
good agreement between the TSI for
phosphorus, chlorophyll a, and
transparency, indicating that these variables are strongly
related.
Eutrophic lakes (TSI 50–70) are characteristic of green
water most of the summer. "Eu" means true and the root
"trophy" means nutrients therefore, eutrophic literally
means true nutrients or truly nutrient rich (phosphorus).
Eutrophic lakes are usually shallow, and are found near
fertile soils. Eutrophic lakes usually have abundant
aquatic plants and algae.
100
Hypereutrophic
70
Eutrophic
50
Mesotrophic
40
Oligotrophic
0
Figure 10. Trophic state index chart with
corresponding trophic status.
Table 7. Trophic state index attributes and their corresponding fisheries and recreation characteristics.
TSI
Attributes
Fisheries & Recreation
<30
Oligotrophy: Clear water, oxygen throughout
Trout fisheries dominate
the year at the bottom of the lake, very deep
cold water.
30–40
Bottom of shallower lakes may become anoxic
Trout fisheries in deep lakes only. Walleye,
(no oxygen).
Cisco present.
40–50
Mesotrophy: Water moderately clear most of
No oxygen at the bottom of the lake results in
the summer. May be "greener" in late summer.
loss of trout. Walleye may predominate.
50–60
Eutrophy: Algae and aquatic plant problems
Warm-water fisheries only. Bass may
possible. "Green" water most of the year.
dominate.
60–70
Blue-green algae dominate, algal scums and
Dense algae and aquatic plants. Low water
aquatic plant problems.
clarity may discourage swimming and boating.
70–80
Hypereutrophy: Dense algae and aquatic
Water is not suitable for recreation.
plants.
>80
Algal scums, few aquatic plants
Rough fish (carp) dominate; summer fish kills
possible
Source: Carlson, R.E. 1997. A trophic state index for lakes. Limnology and Oceanography. 22:361-369.
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Trend Analysis
For detecting trends, a minimum of 8–10 years of data, with 4 or more readings per season, are
recommended. Minimum confidence accepted by the MPCA is 90%. This means that there is a 90%
chance that the data are showing a true trend and a 10% chance that the trend is a random result of
the data. Only short-term trends can be determined with just a few years of data, because there can
be different wet years and dry years, water levels, weather, etc., that affect the water quality naturally.
There was enough historical data to perform trend analysis for total phosphorus, chlorophyll a, and
transparency on Rush Lake. Site 205 had over 8 years of transparency data, which was enough data
to perform a long-term trend analysis using the Mann Kendall Trend Analysis.
Table 8. Trend analysis for Rush Lake.
Lake Site Parameter
Date Range Trend
205
Total Phosphorus
1996–2011
No Trend
205
Chlorophyll a
1996–2011
No Trend
205
Transparency
1996–2011
No Trend
14
Transparency Trend for Rush Lake
Site 204
Site 205
12
Depth (ft)
10
8
6
4
2
0
Figure 11. Transparency (ft) trend for sites 204 and 205 from 1985–2011.
Site 205 shows no significant evidence of a trend in water quality. This means the water quality is
stable (Figure 11). Transparency monitoring should continue so that this trend can be tracked in
future years.
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Ecoregion Comparisons
Minnesota is divided into 7 ecoregions based on land
use, vegetation, precipitation, and geology. The
MPCA has developed a way to determine the
average range of water quality expected for lakes in
each ecoregion. From 1985–1988, the MPCA
evaluated the lake water quality for reference lakes.
These lakes are not considered pristine, but have
little human impact and therefore are representative
of the typical lakes within the ecoregion. The average
range refers to the 25th – 75th percentile range for
data within each ecoregion. For the purpose of this
graphical representation, the means of the reference
lake data sets were used.
Rush Lake is in the Central
Hardwood Forest Ecoregion.
The mean total phosphorus,
chlorophyll a, and
transparency (Secchi depth)
for Rush are all within the
expected ecoregion ranges.
Figure 12. Minnesota Ecoregions.
120
70
0
2
60
4
50
60
40
increased
algae
6
Secchi depth (ft)
80
Chlorophyll-a (ppb)
Total Phosphorus (ppb)
100
40
30
8
10
12
14
20
16
20
crystal
clear
10
18
0
20
0
CHF
Ecoregion
Rush
CHF
Ecoregion
Rush
CHF
Ecoregion
Rush
Figures 13a-c. Rush Lake ranges compared to Northern Lakes and Forest Ecoregion ranges. The Rush Lake
total phosphorus and chlorophyll a ranges are from 97 and 94 data points, respectively, collected in MaySeptember of 1978, 1979, and 1996–2011. The Rush Lake Secchi depth range is from 94 data points collected
in May-September from 1978, 1979, and 1996–2011.
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Lakeshed Data and Interpretations
Lakeshed
Understanding a lakeshed requires an understanding of basic hydrology. A watershed is defined as
all land and water surface area that contribute excess water to a defined point. The MN DNR has
delineated three basic scales of watersheds (from large to small): 1) basins, 2) major watersheds, and
3) minor watersheds.
The Otter Tail River Major Watershed is one of the watersheds that make up the Red River Basin,
which drains north to Lake Winnipeg (Figure 14). This major watershed is made up of 106 minor
watersheds. Rush Lake is located in minor watershed 56035 (Figure 15).
Figure 14. Otter Tail River Watershed.
The MN DNR also has
evaluated catchments for each
individual lake with greater than
100 acres surface area. These
lakesheds (catchments) are the
building blocks for the larger
scale watersheds. Rush Lake
falls within lakeshed 5603500
(Figure 16). Though very
useful for displaying the land
and water that contribute
directly to a lake, lakesheds are
not always true watersheds
because they may not show
the water flowing into a lake
from upstream streams or
rivers. While some lakes may
have only one or two upstream
lakesheds draining into them,
others may be connected to
many others, reflecting a larger
drainage area via stream or
river networks. For further
discussion and information, see
RMB Environmental Laboratories, Inc.
Figure 15. Minor Watershed 56035.
Figure 16. Rush Lakeshed (5603500) with land ownership, lakes, and
wetlands illustrated.
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2012 Rush Lake
page 17. The data interpretation of the Rush lakeshed includes only the land surface that flows
directly into the lake.
The lakeshed vitals table identifies where to focus organizational and management efforts for each
lake (Table 9). Criteria were developed using limnological concepts to determine the effect to lake
water quality.
KEY
Possibly detrimental to the lake
Warrants attention
Beneficial to the lake
Table 9. Rush Lake lakeshed vitals table.
Lakeshed Vitals
Rating
Lake Area
Littoral Zone Area
Lake Max Depth
5234
3511
65
Lake Mean Depth
Water Residence Time
Miles of Stream
Inlets
Outlets
Major Watershed
12
NA
3.7
5
1
56
Minor Watershed
Lakeshed
Ecoregion
Total Lakeshed to Lake Area Ratio (total
56035
5603500
Northern Lakes and Forest
lakeshed includes lake area)
Standard Watershed to Lake Basin Ratio
(standard watershed includes lake areas)
Aquatic Invasive Species
Public Drainage Ditches
Public Lake Accesses
Miles of Shoreline
Shoreline Development Index
Public Land to Private Land Ratio
None as of 2011
None
2
14.8
1.5
0.02:1
Development Classification
Miles of Road
Municipalities in lakeshed
Forestry Practices
Feedlots
Recreational Development
24.1
None
No county forest plan
3
Individual waste treatment systems (last
county inspection in 1994)
None
None
RMB Environmental Laboratories, Inc.
descriptive
descriptive
descriptive
descriptive
79:1
7.5%
Lake Management Plan
Lake Vegetation Survey/Plan
NA
descriptive
2:1
Wetland Coverage
Sewage Management
descriptive
descriptive
descriptive
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Land Cover / Land Use
The activities that occur
on the land within the
lakeshed can greatly
impact a lake. Land use
planning helps ensure the
use of resources in an
organized fashion so the
needs of the present and
future generations can be
best addressed. The
purpose of land use
planning is to ensure
acreage will be used in a
manner that provides
maximum social benefits
without degradation of the
land resource.
Changes in land use, and
ultimately land cover,
impact the hydrology of a
lakeshed. Cover is
directly related to the
land’s ability to absorb
and store water, rather
than cause it to flow
overland (gathering
nutrients and sediment as
it moves) towards the
Figure 17. Rush lakeshed (5603500) land cover (http://land.umn.edu).
lowest point on the
landscape. Impervious
intensity describes the
lands inability to absorb water, the higher the % impervious intensity the more area that water cannot
penetrate in to the soils. Monitoring the changes in land use can assist in future planning procedures
to address the needs of future generations.
Phosphorus export, which is the main cause of lake eutrophication, depends on the type of land cover
occurring in the lakeshed. Figure 17 depicts the land cover in Rush Lake’s lakeshed.
The University of Minnesota has online records of land cover statistics from years 1990 and 2000
(http://land.umn.edu). Although this data is 12 years old, it is the only data set available for comparing
land use over a decade’s time. Table 10 describes Rush lakeshed’s land cover statistics and percent
change from 1990 to 2000. Due to the many factors that influence demographics, one cannot
determine with certainty the projected statistics over the next 10, 20, 30+ years, but one can see the
transition within the lakeshed from agriculture and grass/shrub/wetland, to forest and urban acreages.
The largest change in percentage is the increase in urban cover (55%); however, in acreage, forest
cover has increased the most (398 acres). In addition, the impervious intensity has increased, which
has implications for storm water runoff into the lake. The increase in impervious intensity is
consistent with the increase in urban acreage.
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Table 10. Rush lakeshed’s land cover statistics and % change from 1990 to 2000 (http://land.umn.edu).
1990
2000
% Change
Land Cover
Acres
Percent
Acres
Percent
1990 to 2000
Agriculture
4657
39.19
4274
35.96
8.2% Decrease
Grass/Shrub/Wetland
789
6.64
604
5.08
23.4% Decrease
Forest
931
7.83
1329
11.18
42.7% Increase
Water
5201
43.76
5203
43.78
0.1% Increase
Urban
305
2.57
473
3.98
55.1% Increase
Impervious Intensity %
0
1–10
11–25
26–40
41–60
61–80
81–100
Total Area
Total Impervious Area
(Percent Impervious Area
Excludes Water Area)
11611
46
52
56
81
36
3
97.69
0.39
0.44
0.47
0.68
0.3
0.03
11443
76
120
117
82
30
16
96.28
0.64
1.01
0.98
0.69
0.25
0.13
1.4% Decrease
65.2% Increase
130.8% Increase
108.9% Increase
1.2% Increase
16.7% Decrease
433.3% Increase
11884
97
1.45
11884
139
2.08
43.3% Increase
Demographics
Rush Lake is classified as a recreational development lake.
This type of lake usually has between 60 and 225 acres of
water per mile of shoreline, 3-25 dwellings per mile of
shoreline, and is more than 15 feet deep.
The Minnesota Department of Administration Geographic and
Demographic Analysis Division has extrapolated the future
population of the area, in 5-year increments, out to 2035.
These projections are shown in Figure 18 below. Compared
to Otter Tail County as a whole, Rush Lake and Otto
Townships have a higher extrapolated growth projection.
Figure 18.
Population growth
projection for Rush
Lake and Otto
Township and Otter
Tail County.
(source:
http://www.demogra
phy.state.mn.us/res
ource.html?Id=1933
2)
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Rush Lake Lakeshed Water Quality Protection Strategy
Each lakeshed has a different combination of public and private lands. Looking in more detail at the
makeup of these lands can give insight on where to focus protection efforts. The protected lands
(easements, wetlands, and public land) are the future water quality infrastructure for the lake.
Developed land and agriculture have the highest phosphorus runoff coefficients, so this land should
be minimized for water quality protection.
The majority of the land within Rush lakeshed is made up of agricultural land (Table 11). This land
can be the focus of development and protection efforts in the lakeshed.
Table 11. Land ownership, land use/land cover, estimated phosphorus loading, and ideas for protection and
restoration in Rush lakeshed (Sources: Otter Tail County parcel data, National Wetlands Inventory, and the
2006 National Land Cover Dataset).
Private (55%)
Land Use (%)
Runoff
Coefficient
Lbs of
phosphorus/acre/year
Estimated
Phosphorus
Loading
44%
Public (1%)
Developed
Agriculture
Forested
Uplands
Other
Wetlands
Open
Water
County
State
Federal
3.7%
28.3%
8.9%
3.5%
7.4%
44%
0.4%
0.6%
0%
0.45 – 1.5
0.26 – 0.9
0.09
0.09
0.09
0.09
0.09
197–655
873–3021
96
79
4
7
0
Cropland
Focus of
development and
protection
efforts
State
Forest
National
Forest
Acreage x runoff
coefficient
Description
Potential
Phase 3
Discussion
Items
Focused on
Shoreland
Shoreline
restoration
Restore
wetlands;
CRP
Open,
pasture,
grassland,
shrubland
Forest
stewardship
planning, 3rd
party
certification,
SFIA, local
woodland
cooperatives
Protected
Protected by
Wetland
Conservation
Act
County
Tax Forfeit
Lands
DNR Fisheries Approach for Lake Protection and Restoration
Credit: Peter Jacobson and Michael Duval, Minnesota DNR Fisheries
In an effort to prioritize protection and restoration efforts of fishery lakes, the MN DNR has developed
a ranking system by separating lakes into two categories, those needing protection and those needing
restoration. Modeling by the DNR Fisheries Research Unit suggests that total phosphorus
concentrations increase significantly over natural concentrations in lakes that have watershed with
disturbance greater than 25%. Therefore, lakes with watersheds that have less than 25% disturbance
need protection and lakes with more than 25% need restoration (Table 12). Watershed disturbance
was defined as having urban, agricultural, and mining land uses. Watershed protection is defined as
publicly owned land or conservation easement.
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Table 12. Suggested approaches for watershed protection and restoration of DNR-managed fish lakes in
Minnesota.
Watershed
Watershed
Management
Disturbance
Protected
Comments
Type
(%)
(%)
> 75%
Vigilance
< 75%
Protection
25–60%
n/a
Full Restoration
> 60%
n/a
Partial Restoration
< 25%
Sufficiently protected -- Water quality supports healthy and
diverse native fish communities. Keep public lands protected.
Excellent candidates for protection -- Water quality can be
maintained in a range that supports healthy and diverse native
fish communities. Disturbed lands should be limited to less than
25%.
Realistic chance for full restoration of water quality and improve
quality of fish communities. Disturbed land percentage should
be reduced and BMPs implemented.
Restoration will be very expensive and probably will not achieve
water quality conditions necessary to sustain healthy fish
communities. Restoration opportunities must be critically
evaluated to assure feasible positive outcomes.
The next step was to prioritize lakes within each of these management categories. DNR Fisheries
identified high value fishery lakes, such as cisco refuge lakes. Ciscos (Coregonus artedi) can be an
early indicator of eutrophication in a lake because they require cold hypolimnetic temperatures and
high dissolved oxygen levels. These watersheds with low disturbance and high value fishery lakes are
excellent candidates for priority protection measures, especially those that are related to forestry and
minimizing the effects of landscape disturbance. Forest stewardship planning, harvest coordination to
reduce hydrology impacts, and forest conservation easements are some potential tools that can
protect these high value resources for the long term.
The lake is classified with having 55.5% of the watershed protected and 33.4% of the watershed
disturbed (Figure 19). Therefore, Rush Lake should have a full restoration focus. Goals should
include limiting any increase in disturbed land use and implementing best management practices.
Figure 20 displays the upstream lakesheds that contribute water to the lakeshed of interest. All of the
land and water area in this figure has the potential to contribute water to Rush Lake, whether through
direct overland flow or through a creek or river. Fifty-one of the 112 upstream lakesheds have the
same management focus (full restoration).
Percent of the Watershed Protected
0%
75%
100%
Rush Lake
(55.5%)
Percent of the Watershed with Disturbed Land Cover
0%
25%
100%
Rush Lake
(33.4%)
Figure 19. Rush lakeshed’s percentage of watershed
protected and disturbed.
RMB Environmental Laboratories, Inc.
Figure 20. Upstream lakesheds that contribute water
to the Rush lakeshed. Color-coded based on
management focus (Table 12).
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2012 Rush Lake
Rush, Status of the Fishery (as of 08/16/2010)
Rush Lake is located in central Otter Tail County two miles north of Otter Tail, MN. It is a 5,337-acre
mesotrophic (moderately fertile) lake that is part of the Otter Tail River Watershed. The Otter Tail
River inlet is located along the north shoreline, while the outlet is located along the southwest
shoreline of the lake. The immediate watershed is composed primarily of agricultural land
interspersed with hardwood woodlots and marshes. The maximum depth is 68 feet; however, 62% of
the lake is less than 15 feet deep. The Secchi disk reading during the 2010 lake survey was 4.9 feet.
Previous Secchi disk readings have ranged from 3.5 to 7.0 feet.
A majority of the shoreline of Rush Lake has been developed with homes, cottages, and resorts. The
1998 lake survey referenced 284 homes/cottages and 14 resorts. DNR-owned public water accesses
are located along the northeast and southwest shorelines of the lake.
The shoal water substrates consist primarily of sand and gravel. Large stands of hardstem bulrush
are located along various shorelines of the lake. Emergent aquatic plants such as these provide
valuable fish and wildlife habitat, and are critical for maintaining good water quality. These plants
protect shorelines and lake bottoms, absorbing and breaking down pollutants. Emergent plants
provide spawning areas for fish such as northern pike, largemouth bass, and panfish. They also
serve as an important nursery area for all species of fish. Due to their ecological value, emergent
plants may not be removed without a DNR permit.
Rush Lake is a popular angling lake during both the open water and ice fishing seasons, with a
reputation as one of the best fishing lakes in Otter Tail County. Northern pike, walleye, largemouth
bass, black crappie, and bluegill are the dominant species in the fish community. The prolificacy of
these species can be attributed to the abundance of suitable spawning habitat available. Walleye is a
primary management species in Rush Lake. With a historically high abundance, walleyes ranged in
length from 7.5 to 28.0 inches with an average length and weight of 13.4 inches and 0.9 pounds. The
2006, 2007, and 2008 year classes appear to be strong and should provide good, consistent angling
for several years. Age data from recent lake surveys indicate that the natural reproduction is
substantial enough to consistently maintain the walleye population at or above DNR management
goals. Walleyes attain an average length of 14.8 inches at four years of age.
Northern pike abundance has historically remained at a low to moderate density. The size structure
of the population has consistently been poor. Pike ranged in length from 12.7 to 29.2 inches with an
average length and weight of 19.7 inches and 1.8 pounds. They exhibit moderate growth with an
average length of 22.4 inches at four years of age.
The bluegill test-net catch rate has historically remained stable, with size structure improving over the
recent series of surveys. Thirty-three percent of fish in the trap net sample were 7.0 inches or greater
in length. Bluegills exhibit good growth rates with an average length of 7.2 inches at six years of age.
Summer test-net indices are not reliable indicators of largemouth bass or black crappie abundance
and size structure; however, fishing reports have been positive. Anglers can maintain the quality of
fishing in Rush Lake by practicing selective harvest. This management practice encourages the
release of medium to large-size fish while allowing the harvest of more abundant, smaller fish for table
fare. Releasing the medium to large fish will ensure the lake has enough spawning-age fish annually
and will provide anglers with more opportunities to catch large fish in the future.
See the link below for specific information on gillnet surveys, stocking information, and fish
consumption guidelines. http://www.dnr.state.mn.us/lakefind/showreport.html?downum=56014100
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Key Findings / Recommendations
Monitoring Recommendations
Transparency monitoring at 205 should be continued annually. It is important to continue monitoring
weekly, or at least bimonthly, every year to enable annual comparisons and trend analyses. Site 205
has continuous transparency data back through 1996. Prior to that year, readings were taken at
different sites during different years. It is important to record the Secchi disk readings in the same
location every year, as depth and proximity to aquatic vegetation can affect transparency. If
comparison is desired between sites, monitoring should take place at both sites 204 and 205
annually.
Overall Conclusions
Rush Lake is a shallow, natural eutrophic lake (TSI=52) with no significant water quality trends. Its
lakeshed could use additional protection. One percent (1%) of the lakeshed is in public ownership,
and 55% is protected, while 33% is disturbed (Figure 21). The protection in the lakeshed is somewhat
misleading because it includes the lake’s area, which is 44% of the lakeshed.
Rush Lake has a very large watershed (watershed to lake area ratio of 79:1), and much of the
immediate upstream watershed has disturbed land uses. These land uses are mostly urban and
agricultural.
Rush Lake is a popular angling lake during both the open water and ice fishing seasons. The lake has
a reputation as one of the best fishing lakes in Otter Tail County. The prolificacy of fish species can
be attributed to the abundance of suitable spawning habitat. Emergent aquatic plants, such as
hardstem bulrush, provide valuable fish and wildlife habitat, and are critical for maintaining good water
quality.
Priority Impacts
There are four priority impacts to Rush Lake. The first is additional development, including the second
tier, which adds impervious surface to the lakeshed. The first tier of the lakeshore is already highly
developed everywhere, except in wetlands that abut the shoreline. From 1990–2000, the urban area
around the lake increased 168 acres, and the impervious surface increased by 42 acres. This is a
major change in development.
Agriculture surrounds the lake, and in some areas appears to extend right to the lake without a buffer
(Figure 17). This area could be contributing nutrient runoff to the lake.
Because Rush Lake is a shallow lake, it is very important to protect native aquatic plant beds to
preserve fish habitat and water clarity.
Due to its shallow depths, the lake could also be subject to internal loading. This occurs when the
phosphorus that is in the lake sediment re-suspends into the water column, feeding algae and plants.
Phosphorus re-suspends when large boat motors churn up the sediment, followed by calm days
which allow the water to loosely stratify, and then windy days, which mix the water back up. The
dissolved oxygen profiles show that the lake mixes often in the summer, and the phosphorus figure
indicates that phosphorus increases as the summer progresses (Figures 7 & 9).
Best Management Practices Recommendations
The management focus for Rush Lake should protect the water quality. Restoration efforts should be
focused on managing and/or decreasing the impact caused by additional development, including
second tier development, and impervious surface area. Project ideas include protecting land with
conservation easements, enforcing county shoreline ordinances, smart development, shoreline
restoration, rain gardens, and septic system maintenance.
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On-the-ground inspection along the lakeshore would determine whether the agriculture is draining into
the lake. If so, the area would benefit greatly by partnering with farmers to implement conservation
farming practices, increase shoreline buffers, and/or place priority parcels into land retirement
programs to decrease the impacts of agriculture in the lakeshed.
Native aquatic plants stabilize the lake’s sediments and tie up phosphorus in their tissue. When
aquatic plants are uprooted from a shallow lake, the lake bottom is disturbed, and the phosphorus in
the water column gets utilized by algae instead of plants. This contributes to greener water and more
algae blooms. Protecting native aquatic plant beds will ensure a healthy lake and healthy fishery.
Project Implementation
The best management practices above can be implemented by a variety of entities. Some possibilities
are listed below.
Individual property owners
Shoreline restoration
Rain gardens
Aquatic plant bed protection (only remove a small area for swimming)
Lake Associations
Lake condition monitoring
Internal loading monitoring
Ground truthing – visual inspection upstream on stream inlets
Watershed mapping by a consultant
Shoreline inventory study by a consultant
Soil and Water Conservation District (SWCD) and Natural Resources Conservation Service (NRCS)
Shoreline restoration
Stream buffers
Work with farmers to
o Restore wetlands
o Implement conservation farming practices
o Participate in land retirement programs such as Conservation Reserve Program
Organizational Contacts and Reference Sites
Rush Lake Association
http://www.fishrushlake.com/rushlakeassocation.html
DNR Fisheries Office
1509 1st Avenue North, Fergus Falls, MN 56537
218-739-7576
[email protected]
http://www.dnr.state.mn.us/areas/fisheries/fergusfalls/index.html
Regional Minnesota Pollution
Control Agency Office
714 Lake Ave., Suite 220, Detroit Lakes, MN 56501
218-847-1519, 1-800-657-3864
http://www.pca.state.mn.us/yhiz3e0
Regional Board of Soil and Water
Resources Office
801 Jenny Ave SW Suite 2, Perham, MN 56573
Phone. 218-346-4260 ext.3
http://www.eotswcd.org/
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Surface Runoff Analysis
This analysis is for Rush Lake. This
process utilizes new laser elevation data
and computer applications to evaluate
landscape shape and position. The
output is a relative threat number that
equates to the likelihood of pollution
reaching the lake from that location.
Current land use is not incorporated into
this analysis.
Steve Henry
Douglas County Water Resource Technician
8/15/2012