SPRINGFIELD – As temperatures begin to rise, the Illinois Environmental Protection Agency and Department of Public Health are reminding residents to be cautious if they are planning activities on Illinois lakes and rivers, now and throughout the summer. Water conditions are ideal for cyanobacteria growth. Cyanobacteria (also known as blue-green algae) are microscopic organisms that naturally occur in lakes, streams, and ponds. Rapid and expansive growth of cyanobacteria is referred to as a “bloom.” While most blooms are harmless, some can produce toxic chemicals that cause sickness or other health effects in people and pets, depending on the amount and type of exposure.

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Sensitive individuals, including young children, the elderly, and people with compromised immune systems are most at risk to adverse health effects attributable to algal toxins. Individuals are most often exposed to algal toxins while swimming or participating in other recreational activities in and on the water. The most common routes of exposure are direct skin contact, accidental ingestion of contaminated water, or accidental inhalation of water droplets in the air (e.g., while water skiing). Symptoms of exposure to algal toxins include rashes, hives, diarrhea, vomiting, coughing, or wheezing. More severe symptoms may result from longer or greater amounts of exposure. If you are concerned you have symptoms that are a result of exposure to algal toxins, contact your health care provider or call the Illinois Poison Center at 1-800-222-1222.

Residents are reminded to use caution when recreating in or on Illinois waterways, as cyanobacteria blooms are possible throughout the year. When a bloom producing toxins has been confirmed, local officials are advised to post appropriate signage to warn residents to avoid contact with affected waters; however, not all blooms are reported to state officials. Therefore, residents must be aware and avoid contact with suspicious looking water. Residents who plan to recreate in or on Illinois waters are advised to avoid contact with water that:

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• looks like spilled, green or blue-green paint;
• has surface scums, mats, or films;
• has a blue or green crust at the shoreline;
• is discolored or has green-colored streaks; or
• has greenish globs suspended in the water below the surface.

People are also advised to keep pets out of the water. Do not allow pets to drink from the water and do not allow them to lick their fur after swimming in water containing a cyanobacteria bloom. If you or your pet has contact with water you suspect may have a cyanobacteria bloom, rinse off with clean, fresh water as soon as possible. If your pet experiences symptoms that may be the result of exposure, contact your veterinarian immediately.

Activities near, but not in or on a lake or river, such as camping, picnicking, biking, and hiking are not affected. With all activities, wash your hands with soap and water before eating if you have had contact with lake water or shore debris.

For additional information about harmful algal blooms, please visit the Illinois Environmental Protection Agency Harmful Algal Bloom website:

U.S. EPA’s Cyanobacterial Harmful Algal Blooms website:

Read More:

May 27, 2016 | Illinois urges caution while recreating in Illinoois lakes or rivers with blue-green algae May 27, 2016

Sep 23, 2020 | Illinois Officials Ask Residents to Continue to be Alert to Possible Blue-Green Algae on Illinois Lakes, Rivers, Streams & Ponds Sep 23, 2020

Jul 2, 2018 | Follow-up samples from the Illinois River show no microcystins Jul 2, 2018

Jun 17, 2021 | Illinois Officials Confirm Algal Bloom on Portions of the Illinois River Jun 17, 2021

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