Algonquin
Lakes
WWW.SBAA.CA
Many visitors to Algonquin Park come here for the canoeing.
Algonquin covers 7725 km2 and has over 2100 kilometres
of canoe routes. Surprisingly, lakes make up only 10% of
Algonquin Park. While many Park visitors use Algonquin’s
lakes for canoeing, swimming, fishing or just admiring, they
are often overlooked as one of Algonquin’s major habitats.
Most people think of the lakes here as a place for loons to
call home during the summer and where fish swim about. In
fact, there is a very complex world beneath the waves.
Distribution of lakes and
rivers in Algonquin Park
shown in blue.
While it can be said that there are two Algonquin Parks (the
Highway 60 Corridor and the Park Interior), it can also be
Highway 60 shown in red.
said that each lake is actually two lakes in one. That is, there
is a warm lake and a cold lake, one sitting on top of the other.
This phenomenon occurs in all Algonquin’s lakes and has a great effect on the living and non-living
matter in them.
The process of getting two lakes starts in the spring.
Over the winter, the water near the surface under
the ice has been close to freezing. The rest of the
lake has had a temperature of 4˚C, the temperature
at which water is the heaviest. Once the lake has
become clear of ice in the early spring, the top
layer of water gradually starts to warm until the
entire lake is at a uniform 4˚C. All levels of the
lake now share the same characteristics, an
important one being the resistance to currents. As
the winds of spring blow across the surface of the
lakes creating waves, an important process is taking place beneath the surface. The motion of the
waves creates currents and because the entire lake now has the same resistance to currents the lake
circulates from top to bottom mixing everything in it. This phenomenon is known as the spring turnover
and may last for several days, during which the temperature of the lake gradually increases.
WWW.SBAA.CA
Eventually the surface water becomes warmer and the wind has a harder time mixing the warm water
with the cold water. If there is a period of a few
days where there is little or no wind the surface
water is able to warm up enough that even the
strongest wind will not be able to mix this lighter
water with the colder, heavier water several metres
below. This signals the end of the spring turnover.
The surface water is only able to absorb heat down
to about four metres. In this range the wind still
creates currents mixing the water, creating a
uniform temperature down to four metres. Below
four metres the temperature drops off quickly and
is homogeneously cold down to the bottom. The
lake is now divided into two separate entities, a
warm upper lake and a cold lower lake, with a
narrow transition zone between the two. Each part
now acts separately with no mixing taking place
between the two. The top layer continues to
circulate and warm up through the summer months
while the bottom layer stays as cold as it did during
the spring turnover. The temperature differences
between the two layers can be as much as 15˚C.
The lake stays this way until late September or
October when the upper lake begins to cool down.
When it has reached the same temperature as the
lower lake the resistance to currents between the
two layers is the same and the entire lake begins to mix again. This is known as the fall turnover and
continues until the lake starts to freeze over sometime in December.
WWW.SBAA.CA
These turnovers in the spring and fall gives a lake two breaths of air that help sustain the animal life
within. The air that we humans breathe contains 21% oxygen while a lake only contains 1% oxygen.
Oxygen from green plants does contribute to some of the oxygen in a lake but the main source is the
wave action that helps put oxygen into the lake twice a year. As mentioned above, the spring and fall
turnovers circulate everything right from top to bottom, mixing everything thoroughly. As well, cold
water holds more oxygen than warm water so during the spring and fall a lake can take on the maximum
amount of oxygen possible. This is important for two reasons. During the summer when a lake gets
divided into its two zones the lower colder zone is effectively cut off from any air in the warm upper
layer. Thus, the cold bottom layer only has oxygen carried to it by the spring turnover. No oxygen is
added to this layer during the summer and a lake has to wait until the fall turnover to get another
infusion of oxygen. Plants, animals, and decaying matter continue to use up oxygen year-round. During
the summer the oxygen levels can vary greatly between the top and bottom of a lake. This can be a
problem for any coldwater-dwelling animals that are trying to survive in the lower areas of a lake.
The fall turnover is very important for a lake. This last big breath of air that a lake takes before ice-up
has to last all winter. Fish and plants continue to use oxygen but an even bigger consumer of oxygen is
decaying of plants and animals. On rare occasions a shallow lake that has a great deal of decaying
matter may use up all its oxygen before it can get another influx of oxygen in the spring, resulting in a
large die-off of the resident fish species.
Although plants in a lake are minor contributors to the oxygen levels of a lake their presence is important
to the overall survival of the lake. Just as with terrestrial plants, water plants are the foundation for
other forms of life. If water plants are not able to obtain the basic necessities for their survival then
animals that depend on the plants also will not be able to survive.
Green plants are able to generate their own food by utilizing sunlight and carbon dioxide. They also
need other nutrients such as nitrogen, potassium and phosphorus to survive. These nutrients need to be
present in the water for the plants to survive. All these nutrients come from the surrounding soil and are
washed down into the lake. Nitrogen is present in the atmosphere but cannot enter the soil or water
WWW.SBAA.CA
directly as does oxygen or carbon dioxide. Instead the nitrogen is converted to ammonia or nitrates
through a complex cycle where it is then present in the soil and can be washed into the lake.
The other nutrients are obtained directly from the rocks surrounding a lake. If the rocks are rich in
nutrients, and can be easily released into a lake, they will have a great influence on the level of plant
life. In turn, this will have an effect on the number of smaller animals and fish.
Algonquin Park, though, has rocks with very low nutrients. In turn, the rocks are very hard and thus
give up their meagre nutrients very slowly. This means that the growth of water plants is limited. In
turn, this limits the number of small fish which then directly affects the growth rate of bigger game fish
such as Lake Trout.
Most people think of water plants as the large plants, such as water-lilies and different pond weeds.
These are the plants that inhabit the shallower areas of a lake where they can grow in the available
sunlight and take root. Growing on these plants are smaller plants. This slimy layer is algae, and the
large plants they grow on make up a large part of the vegetation of a lake, but they are limited to the
shallow areas.
Light penetration on a lake is limited to the top few metres and this is the only place where plants can
grow. Aside from the shallows, it would appear that this is the only area of a lake where plants could
grow. There are actually millions of plants growing in the open waters of Algonquin’s lakes. These
microscopic plants are free-floating algae. There are several different kinds, varying in shape, which
occupy different depths of the sunlit portion of a lake. Their numbers vary from season to season but
they are most abundant during the spring and fall turnovers.
These millions of invisible basic, plants and their larger relatives are a very important part of an Algonquin
lake and supporting all the animals living there.
As in Algonquin’s forests, where the producers are eaten by primary consumers that are thus eaten by
secondary consumers that then may be eaten by tertiary consumers, so does the chain exist in Algonquin’s
WWW.SBAA.CA
lakes. The free-floating, microscopic algae are consumed by several types of small animals. One of the
most common is the rotifers or “wheel animals”. Two other major algae eaters are crustaceans, the
water fleas, and copepods. All three of these small, underwater animals feed on the algae by filtering it
from large quantities of water.
Other larger, algae-eaters live in the shallower parts of a lake. Snails feed on the algae of the stems and
leaves of water plants and Mayfly larvae, and other insects, feed on algae scum.
Even in the depths of Algonquin’s lakes there are tiny animals that feed on dead and decaying plant
matter. Midge larva spends most of its life partially buried in the mud where it feeds on dead plants and
animals that float to the bottom.
Within an Algonquin lake there can be several species of minnows, each one having a different life
history and occupying a different niche from its neighbour. The Red Bellied and Pearl dace both inhabit
the same quiet areas of a lake with lots of organic matter, but each utilizes a different food source. The
Red Bellied Dace eats mainly algae, while the Pearl Dace feeds mainly on water fleas and small insect
larvae. So while these two minnows live in the same habitat they are not competing with each other for
food.
Another type of minnow that inhabits Algonquin’s lakes but utilizes a completely different niche is the
Golden Shiner. It also eats small animals but prefers the waters away from shore, exploiting the available
food source at or just underneath the surface.
Algonquin’s lakes may have a few other species of larger fish. The Pumpkinseed, or sunfish, is an
inhabitant of the shallow areas of lakes where it feeds on snails, dragonfly nymphs, and even young
salamanders.
Yellow Perch can also be found in some lakes, usually in shallow, open water, with moderate vegetation.
Young perch will feed on smaller prey such as insect larvae, eventually moving to large invertebrates
and minnows as they become bigger.
WWW.SBAA.CA
These smaller fish are an important food source for the larger game fish. Three species dominate
Algonquin’s lakes and are present, to one degree or another, in all but a few lakes. Two native species
found in Algonquin are the Lake Trout and Brook Trout (often called Speckled Trout). Despite its
name, the Brook Trout, like the Lake Trout, inhabit Algonquin’s cold, deep lakes. Unfortunately, some
Brook Trout populations in Algonquin Park have been eliminated due to the introduction of Smallmouth Bass. Introduced as a viable game fish by Park authorities in 1899, the Small-mouth Bass outcompeted native Brook Trout for food.
There are fifty recorded fish species in Algonquin Park, and there are numerous anglers who exploit
this fish life as a food source. These are not human anglers that frequent lakes from spring to fall, but
different birds and mammals that largely depend on Algonquin’s fish to survive. Mammals such as
River Otter and Mink, and birds like the Belted Kingfisher, Osprey, and Common Mergansers, all prey
on the different fish species in Algonquin’s lakes. The most successful though is the Common Loon
which is adapted to diving and hunting fish. While the loon and other fish-eaters are at the top of a
lake’s food chain, they are all dependent on the microscopic algae that are ultimately the life source of
all other organisms within a lake.