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Harmful Algal Blooms (HABs) and Algal Toxins

What are Blue-Green Algae?

Blue-green algae are microscopic organisms that occur naturally in Illinois lakes and streams. Despite their name, blue-green algae are actually types of bacteria known as cyanobacteria. When certain conditions are present, such as high nutrient and light levels, these organisms can reproduce rapidly. This dense growth of algae is called a “bloom.” Blue-green algal blooms can discolor the water or produce floating scums on the surface of the water, especially along shorelines. While blooms can occur at any time of year, they are primarily a concern during the summer months because that is when people are likely to come in contact with them.

Algal Bloom Sampling

What are Harmful Algal Blooms?

While most blue-green algal blooms are not harmful, some can be. Under certain conditions that are not well understood, some blue-green algae are capable of producing algal toxins that could pose a health risk or harm people and animals when exposed to them in large enough quantities (Harmful Algal Blooms, or “HABs”).

Is there a Concern about Algal Toxins in Illinois?

Yes. While there are many different known algal toxins, the most common one found in Illinois is called microcystin, a known liver-damaging toxin. Adverse health effects could occur when waters exhibiting a blue-green algal bloom are swallowed, come in contact with skin, or when airborne droplets containing toxins are inhaled while swimming, boating, waterskiing, tubing, bathing or showering. Pets are also at risk when allowed to drink or swim in surface water containing a blue-green algal bloom. Health effects can include asthma-like symptoms, abdominal pain, vomiting, diarrhea, rashes, or nervous system effects depending on the exposure level and type of toxin present in the water.

Monitoring conducted by the Illinois Environmental Protection Agency (Illinois EPA) from 2005-2008 showed that microcystin was frequently detected in Illinois lakes and streams (50.5% of the samples collected), but concentrations were generally below levels of concern. Unfortunately, monitoring conducted during the 2012 summer drought revealed a different story. (See "2012 Drought and HAB Reconnaissance Monitoring Effort")

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.

People Pets
Do not swim or wade through algal scums. Do not let dogs drink lake water during an algal bloom.
Do 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. Wash 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.  

Learn More...

Harmful Algal Bloom Menu

Harmful Algal Blooms (HABs) and Algal Toxins
Identifying and Reporting Harmful Algal Blooms (HABs) in Illinois
Harmful Algal Bloom Report Form
2012 Drought and HAB Reconnaissance Monitoring Effort
Working Together Toward a Statewide Harmful Algal Bloom Program in Illinois
Statewide Harmful Algal Bloom Program Initiated in 2013
Links to Other Resources
Contact Information For Further Assistance
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