Harmful Algal Blooms in Ohio's Inland Lakes

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Harmful Algal Blooms

Information for Campground Operators and Privately-Owned Lakes and Ponds (pdf)

Information and Monitoring Data

Cyanobacteria, often called blue-green algae, are bacteria that are naturally found in Ohio lakes, ponds, and slow-moving streams. Although many species of algae do not produce toxins, some species of blue-green algae can cause Harmful Algal Blooms (HABs). 

Several of Ohio’s inland lakes have experienced cyanobacteria blue-green algae blooms.

Depending on the genera, water conditions, and other factors, neurotoxins, hepatotoxins, cytotoxins, dermatotoxins and gastrointestinal toxins can be produced by cyanobacteria. These toxins are released to the water as the bacteria die. Water samples from various Ohio lakes have detected the presence of microcystin, anatoxin-a, cylindrospermopsin and saxitoxin. Both humans and animals can experience illness from exposure to these toxins during recreational activities and other water uses.

Under the right water conditions, which usually occur in the warmer months, the number of these blue-green algae can dramatically increase, or “bloom.” Scientists do not fully understand what causes the same species of algae to trigger toxin production during one bloom and not produce toxin during the next. 

Some cyanobacterial blooms can look like foam, scum, or mats on the surface of fresh water lakes and ponds. The blooms can be blue, bright green, brown, or red and may look like paint floating on the water. Some blooms may not affect the appearance of the water.

Humans and pets can get sick from exposure to cyanobacteria toxins. The development of illness will depend on the type of cyanobacteria, the levels in the water and the type of contact an individual has had with this “algae.” 

The World Health Organization set guidelines for microcystin toxin (a toxin produced by cyanobacteria) at 1 part per billion (ppb) in drinking water and 20 ppb for recreational waters. Currently, no similar guidance exists for the other toxins produced by cyanobacteria.

What types of health problems can people and pets experience from exposure to high numbers of Blue-Green Algae and HABs?

  • Skin contact: Contact with the skin may cause rashes, hives, or skin blisters (especially on the lips and under swimsuits).
  • Breathing of water droplets: Breathing aerosolized water (suspended water droplets-mist) from the lake, related recreational activities and/or lawn irrigation can cause runny eyes and noses, a sore throat, asthma-like symptoms, or allergic reactions.
  • Swallowing water: Swallowing HAB-contaminated water can cause:
    • Acute (immediate), severe diarrhea and vomiting
    • Liver toxicity (abnormal liver function, abdominal pain, diarrhea and vomiting)
    • Kidney toxicity
    • Neurotoxicity (weakness, salivation, tingly fingers, numbness, dizziness, difficulties breathing, death)      

How to protect yourself, your family, and your pets from exposure to HABs:

  • Don’t swim, water-ski, or boat in areas where the blooms are occurring – avoid direct contact with the lake water or aerosolizing the water.
  • Don’t water lawns, gardens, or golf course with water from HAB-impacted lakes or ponds.
  • Report unpleasant tastes or smells in your drinking water to your local water utility.
  • Follow posted water body closures announced by state agencies or local public health authorities.

How to treat people or animals that have been exposed to HAB toxins:

  • If you do come into contact with the HAB –contaminated water, rinse off with clean, fresh water as soon as possible. 
  • Pets that have been swimming in an area with an algae bloom may ingest significant amounts of toxins by licking their fur after leaving the water. Thoroughly rinse off your pets with clean, fresh water.
  • Seek medical treatment ASAP if you think you, your pet, or your livestock might have been poisoned by toxic HABs.
  • Remove people from the exposure and seek medical treatment if symptoms occur.

For more information on Harmful Algal Blooms please visit:


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