Blue-green algae are not always blue!
Blue-green algae most often look like tiny green particles mixed into lake water. At low
concentrations in the water, they won’t be quite as dense as shown in this image, which was
photographed in a shallow dish. You might see concentrations in a lake similar to this image if
algae numbers are higher and wave action is keeping the water mixed.
G. LaLiberte
If weather is calm, blue-green algae can float to the surface and start to form a scum.
These scums are blown around by wind and can accumulate close to shore.
Duckweed – look for roots
Blue-green algae – looks like
pale green floating dust as it
starts to form a scum.
Actively growing blue-green algae are
usually green to light green in color.
G. LaLiberte
actively growing
blue-green algae
decomposing blue-green algae
- pigments are released
These photos show very
concentrated blue-green algae.
Keep kids & dogs out if it looks
like this! Actively growing bluegreen algae is usually green, while
other colors appear when bluegreen algae decompose.
M.
M.Meade
Meade
Actively growing blue-green algae are
usually green to light green in color.
J. Williamson
T. Moris
Don’t mistake duckweeds, watermeal, or pollen for blue-green algae
Duckweeds (Lemna,
Spirodela) have roots.
Lemna, Spirodela, Wolffia
Watermeal (Wolffia) is
tiny, firm, and grainy
in texture. Wolffia are
oval or doubled ovals
in shape.
G. LaLiberte
G. LaLiberte
Watermeal (Wolffia)
G. LaLiberte
Pollen looks like floating yellow dust.
Look for similar yellow “dust” on land,
especially on cars parked under trees.
G. LaLiberte
Microcystis Planktonic (floating) blue-green algae)
Most common bloom-former in Wisconsin. Round to irregularly shaped colonies.
Aphanizomenon
Planktonic (floating) blue-green algae)
Look like tiny grass clippings
C. Carlson
Gloeotrichia
Planktonic (floating) blue-green algae)
Pinhead-sized balls; can bloom in lakes with low to moderate nutrient levels
Some blue-green algae grow on lake bottoms in mats and may float to the surface. Some
species are brightly colored. Filaments are usually very narrow and short, less than a quarter
inch in length. Avoid swimming through these floating mats, and don’t let dogs eat them.
Small floating mats
filaments
Don’t mistake filamentous green algae for bluegreen algae.
G. LaLiberte
Looks like long green hair if you lift it out of the water.
Blue-green algal mats are usually darker in color than
filamentous green algae
G. LaLiberte
G. LaLiberte
filamentous green algae mats
G. LaLiberte
Starts on the bottom
resting cells
G. LaLiberte
Floats to the top via O2 bubbles
Reproduces, makes
resting cells, decays.
Lake Monona, Dane County. June 2, 2015.
Both photographs were taken within 1 hour of each other at sites 3 miles apart.
Blue-green algal blooms can be very patchy and change rapidly as wind blows them around
lakes. If you can’t see your feet in knee-deep water, like in the photo on the right, algae densities
are high enough to make you sick if you swallow the water. Keep small children and dogs out!
Even in good water conditions, wash off after swimming and always wash dogs with clean water
immediately after they swim, before they groom themselves.
Always avoid swallowing untreated surface water – it may contain bacteria, viruses, and
parasites which could make you ill. Bacteria numbers may be high for several days after heavy
rains.
More resources:
http://dnr.wi.gov/lakes/bluegreenalgae
https://www.dhs.wisconsin.gov/water/bg-algae/defined.htm
Have questions?
Gina LaLiberte – WDNR
608-221-5377
[email protected]