What are blue-green algae?
Many species of algae are found in Wisconsin lakes and rivers. Algae act
like other plants and convert sunlight into energy, forming the base of a
lake’s food chain. Algae are eaten by zooplankton, which are in turn
eaten by small fish, then larger fish, and eventually the larger fish are
eaten by birds, shore animals, and people. True algae are a vital part of
lake systems, however, blue-green algae are not true algae. Blue-green
algae are photosynthetic bacteria known as cyanobacteria which can cause
illness and death in humans and animals. While blue-green algae can
convert sunlight into energy, they are not an important a part of the food
chain because most organisms prefer not to eat them.
Blue-green algae are a natural part of lake ecosystems and algal blooms
have occurred for many centuries. While scientists are learning more
and more about blue-green algae, researchers are only beginning to
understand the health risk blue-green algae pose to humans and animals.
What are algal blooms and why do they occur?
When environmental conditions are right, the algal population can grow quickly
and a bloom can occur. A bloom is a sudden increase in algae cells in a certain area
of water. Little wind, warm water, sunlight, and plentiful nutrients
–especially phosphorus- all increase the chance that a bloom will
occur. Warm weather patterns and large rain events that wash agricultural and
residential fertilizers (which contain phosphorus) into the water can also jump start a bloom.
In Wisconsin, blooms typically occur during the warm weather months between mid
June and mid September. Lakes and rivers in Wisconsin can become cloudy with rapidly
reproducing algae. Blue-green algae will follow sunlight and nutrients by floating to the surface where
they can form thick scum layers or mats and the surface may look
bubbly or frothy. Algal scums can be pushed to different locations by wind or tide. When
blue-green algae are present, the algal scum can be a variety of colors such as fluorescent blue, green, white, red or
brown. Blooms can have more than one color present and may look like thick paint floating on the water.
Algal blooms can give off a foul odor, which is particularly
offensive in the warm summer months.
What should I do if I see a bloom?
People should use common sense when dealing with algae. It is impossible to tell from a visual inspection whether an algal bloom is
toxic. The safest thing to do is to treat every algal bloom as if it could be dangerous.
Do not swim or wade through algal scums.
|Do not let dogs drink lake water during an algal bloom.
not boat, water ski or jet ski through algal blooms.
||Do not let dogs eat algal scum, or lick it off their fur.
|Do not fish
from lakes where algal scum is present.
your dog off with clean water immediately if your dog swims or
wades in water during an algal bloom.
|Always shower off with soap and water after swimming in a lake.
illness to the Wisconsin
Harmful Algal Blooms Program.
Back to Environmental Health Resources
Last revised: March 03, 2011