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Harmful Algal Blooms (HABs)

          Grand Lake St Marys boat dock with HABs                             
What are HABs?

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). 
 is a one-stop shop for algae information in Ohio. Visit it to find information on the following HAB topics:

  • View a list of current advisories or sampling data
  • Report potential algal blooms
  • Get tips about HABs

Ohio has developed standards for the posting of Ohio Recreational Use Advisories.

The public health advisory would be posted when tests conclude microcystin levels are at least six parts per billion (ppb).  At this point, the public would be advised that swimming and wading are not recommended, water should not be swallowed and surface scum should be avoided.

  • A no contact advisory would recommend the public to avoid all contact with the water at that location.  A no contact advisory would be posted if test results show microcystin levels at least 20 ppb and there has been a report of human illness or pet death.  If a no contact advisory is posted for a recreational contact area, the State may sample the lake to determine if an open water no contact advisory should be posted.

Once an advisory is posted, Ohio will periodically sample until microcystin is below acceptable thresholds or the end of the beach season in Ohio. 

Click the following hyperlink text to view a map of the current HAB advisories.  


What do HABs look like?

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 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.

Click the following hyperlink text to see photos of HAB outbreaks in Ohio.

Can you smell HABs?

Some of the blue-green algae produce an odor generating byproduct, named geosmin.  The human nose is extremely sensitive to geosmin and is able to detect it at concentrations at very low levels.  These odors are not chemically toxic but do have a very unpleasant smell which can cause sensitive individuals to become nauseous (upset stomach, vomiting) and have headaches.

Click the following hyperlink text to see more information about Odors and Your Health

Can you get sick from exposure to HABs?

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

HABs can produce neurotoxins (which affect the nervous system) and hepatotoxins (which affect the liver).  These toxins can potentially impact the health of people who come into contact with water where HABs are present in high numbers.

The chemical toxins produced by these blue-green algae do not change from a liquid to a gas and they are not released as vapors to the outside air.  However, recreational activities like power boating, water-skiing, jet-skiing and tubing can whip up the surface of the water and create aerosols – toxin-containing water droplets – that can be inhaled or ingested, potentially resulting in negative health effects.  Other activities that have the potential to aerosolize the lake water include using the lake water to irrigate lawns/gardens and golf courses.

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 aerosolizing (suspended water droplets-mist) from the lake water-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 can I protect myself, family and pets from exposure to HABs?

  • Don’t swim, water-ski, or boat at high speeds 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 advisories announced by state agencies or local public health authorities.

How do you 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 a HAB may ingest significant amounts of toxins by licking their fur after leaving the water.  Thoroughly rinse of 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 HAB.
  • Remove people from the exposure and seek medical treatment if symptoms occur.

Click the following hyperlink text to see a copy of the ODH HAB Physician Reference 

Reporting HAB illness:

  • Local health districts should complete forms for reports of human illnesses associated with either recreational or public water supply exposures to a HAB and/or HAB toxin, and then fax completed forms to the Ohio Department of Health (ODH) Bureau of Environmental Health and Radiation Protection (BEHRP) secure fax: 614-466-4556.
  • Completed animal illness report forms should be faxed to the ODH Zoonotic Disease Program (ZDP) secure fax: 614-564-2437. 

Updated: 7/24/15