Harmful Algal Blooms (HABs)

Groups of people who experience illness with similar symptoms after swimming in recreational water should contact their local health department for follow up.

If you suspect a blue-green algal bloom on your lake or on a lake you have visited, you can report it to the Illinois EPA using the HAB report form. This form captures the environmental event and includes fields for the bloom location, size, and various characteristics like odor and color. Pictures of the bloom may also be uploaded. The HAB report form can be found here.

Harmful Algal Bloom FAQs

What are blue-green algae?

Blue-green algae, or cyanobacteria, are photosynthetic bacteria that are a natural part of the aquatic environment. Blue-green algae are often present in Illinois lakes in small or moderate amounts, but can grow and proliferate quickly in warm, fresh water that is rich with nutrients (like nitrogen and phosphorous). This sudden, rapid growth is referred to as an algal “bloom”.

What are harmful algal blooms?

Harmful algal blooms (HABs) are blue-green algae blooms that may adversely affect humans, animals, and the environment. In Illinois, blooms typically occur during the warm-weather months of June through September. Blooms may appear as a thick scum layer or green paint on the surface of the water, and can be a variety of colors such as blue, green, or brown. There may also be a foul odor present during a bloom, especially during the warm summer months.

The production of toxins is what makes an algal bloom harmful. Microcystin is the most well-known toxin produced during a harmful algal bloom, and it can cause a variety of symptoms by affecting the skin, liver, GI tract, and nervous system. Ingestion, inhalation, or direct contact with contaminated water may cause illness.

What causes harmful algal blooms?

Warm water, sunlight, and little wind are ideal conditions for a harmful algal bloom (HAB). If a large amount of nutrients like nitrogen and phosphorus are introduced into the water when conditions are right, a HAB can quickly form. Agricultural or residential fertilizers that contain phosphorus can contribute to the formation of HABs if they are washed into a nearby water body (for example, during a large storm).

What should I do if I see a bloom?

It is impossible to tell from a visual inspection whether an algal bloom is toxic. Avoid the water where the bloom is located, and notify the Illinois EPA of a possible HAB event via the HAB report form.

  • Do not swim or wade through algal scums
  • Do not boat, water ski, jet ski, or fish where algal scum is present
  • Always shower off with soap and water after swimming in a lake, river, or pond
  • Do not let dogs drink, eat, or lick algal scum off their fur
  • Wash your dog off with clean water immediately if your dog swims or wades in water during an algal bloom.