Skip to main content

Identifying Cyanobacteria Blooms

When cyanobacteria (blue-green algae) reproduce quickly and bloom, there are physical signs. The blooms can look like blue or green paint spilled into the water, a blue or green colored crust along the shoreline, thick puffy blue or green foams on the surface of the water (scums), or swirling colors beneath the surface of the water. Blooms can sometimes be white, brown, or red in color. Cyanobacteria blooms can also have distinct smells. They can smell grassy or septic, and in some cases the smell can cause nausea. These cyanobacteria blooms can accumulate near the shoreline and can move based on wind and wave action. Long strands of green algae, duckweed, and filamentous macro-algae are sometimes confused with cyanobacteria blooms. Please visit the gallery below to see some of the different forms cyanobacteria blooms can take and some commonly confused plants that could look like a bloom.  Illinois EPA also has a Harmful Algal Bloom (HAB) Dashboard that displays reported blooms throughout the state.

Cyanobacteria Bloom- Green Water

Cyanobacteria Bloom - Spilled Paint

Cyanobacteria Bloom - Scum

Cyanobacteria Bloom - Globules

Cyanobacteria Bloom - Dried Crust

Cyanobacteria Bloom - Under Ice

Not a Cyanobacteria Bloom