Ohio Algae Information for Recreational Waters

Algal blooms have become more noticeable in Ohio’s lakes, streams and rivers during the last few years.

Although most blooms are green algae and not harmful, there are some that are actually a type of cyanobacteria that have the ability to produce toxins – called harmful algal blooms (HABs).


Remember, you can still boat, fish and recreate in Ohio’s lakes, streams and rivers. Just be aware that HABs exist. We hope the information here will give you a better idea of what HABs can look like and provide you with the information you need to safely enjoy Ohio's waterways.

What is a harmful algal bloom?

A harmful algal bloom (HAB) is a large growth of bacteria that can produce toxins. These toxins may affect the liver, nervous system and/or skin.

What causes HABs to form?

Some factors that can contribute to HABs include sunlight; low-water or low-flow conditions; calm water; warmer temperatures; and excess nutrients (phosphorus or nitrogen). The primary sources of nutrient pollution are runoff of fertilizers, animal manure, sewage treatment plant discharges, storm water runoff, car and power plant emissions and failing septic tanks. The State of Ohio is currently working on a statewide nutrient reduction strategy that will document ongoing nutrient reduction activities and identify areas where more work is needed.

How dangerous are HABs?

If you touch HABs, swallow water with HAB toxins or breathe in water droplets, you could get a rash, have an allergic reaction, get a stomach ache, or feel dizzy or light-headed. HABs also are toxic to pets.

Always look for HABs before going in the water. Check for HAB advisories. Ask the park manager if there has been a recent HAB because colorless toxins can still be in water.

How will I know if there is a HAB?

HABs have different colors and looks. Some colors are green, blue-green, brown, black, white, purple, red and black. They can look like film, crust or puff balls at the surface. They also may look like grass clippings or dots in the water. Some HABs look like spilled paint, pea soup, foam, wool, streaks or green cottage cheese curd.

What should I do if I see a HAB?

  • Stay out of water that may have a HAB.
  • Do not let your children or pets play in HAB debris on the shore.
  • After swimming or wading in lake water, even where no HABs are visible, rinse off with fresh water as soon as possible.
  • Never swallow any lake or river water, whether you see HABs or not.
  • Do not let pets lick HAB material from their fur or eat HAB material.
  • Do not drink or cook with lake water.
  • See a doctor if you or your children might be ill from HAB toxins. If your pet appears ill, contact your veterinarian.
  • Report the bloom to Ohio EPA by completing the report form and emailing it to HABmailbox@epa.ohio.gov.

What about fishing and other activities?

If you plan to eat the fish you catch, remove the guts and liver, and rinse fillets in tap water before eating. Other activities near the water such as camping, picnicking, biking and hiking are safe. If you are picnicking, wash your hands before eating if you have had contact with lake water or shore debris.

The advisory for state park beaches has two levels.

Be alert for these advisories and changing water conditions.

  • Recreational Public Health Advisory
    Recreational Public Health AdvisoryAn orange Recreational Public Health Advisory sign will be posted at beaches when toxin levels exceed the recommended threshold, warning individuals who are elderly or very young and people with compromised immune systems that swimming or wading is not recommended.


  • No Contact Advisory
    No Contact AdvisoryA red No Contact Advisory sign will be posted when toxin levels exceed the recommended threshold and there are one or more probable cases of human illness or pet deaths attributable to HABs. This sign will warn people that unsafe toxins are present in the water and to avoid any contact.

Drinking Water Advisory

If microcystin, anatoxin-a, cylindrospermopsin or saxitoxin is found above drinking water thresholds in the finished water of a public water system, the water system will public notice a drinking water advisory.

Depending on the toxin level detected, either a do not drink or do not use warning will be issued. The public water system may end a public notice when algal toxin levels are below the drinking water thresholds in two consecutive samples collected at least 24 hours apart.

What should I do if my pets or livestock become ill?

Time can be critical — some exposures to HABs can produce life-threatening illnesses within a half-hour of ingestion, while other symptoms may take several hours to days to emerge. Contact your veterinarian immediately if your pet or livestock become ill. Indicate that your animal was in water containing an algal bloom and was drinking the water; eating algae off the beach; or licking algae off its fur/skin while grooming.

What are the symptoms?

According to Dr. Michael Carlson, diagnostic toxicologist with the UNL Veterinary Diagnostic Center at the University of Nebraska, liver toxins such as microcystin can cause lethargy, vomiting, diarrhea, weakness, pale mucous membranes and death. Animals suffering from the nerve toxin, anatoxin-a poisoning, can experience muscle tremors, rigidity, lethargy, respiratory distress, convulsions and death. Victims of the nerve toxin anatoxin-a(s) poisoning can experience salivation, urination, defecation, secretion of tears, tremors, shortness of breath, convulsions and death.

How can I keep my pets and livestock safe?

  • Keep pets and livestock out of water with algal blooms. “When in doubt, keep them out.”
  • Keep livestock fenced out of water with algae blooms.
  • If your pets do enter the water, be sure to rinse them off well so they do not lick algae
    off their fur or skin as toxins may still be present.
  • Do not let your pet eat algae off the beach as toxins may still be present.

Where should I report HAB-related illnesses?

After immediate treatment, report illnesses to the State Veterinarian at (614) 728-6220 or (800) 300-9755.

to learn more about harmful algal blooms and state park beach advisories.

Algal Toxin Results

From Lake Erie, Ohio state park beaches and public water supplies:
Excel file

Report a Bloom

If you see surface scum or something that looks like blue-green algae at a state park lake beach, report it to Ohio EPA by completing the Bloom Report Form (click here for a fillable form) and emailing it to HABmailbox@epa.ohio.gov.


For more information about harmful algal blooms, contact:
Public Interest Center, Ohio EPA
(614) 644-2160

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