Important Information on Harmful Algal Blooms

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Harmful Algal Bloom at Harsha Lake

  What is a Harmful Algal Bloom?

 Harmful algal blooms are formed by a type of blue-green algae known as cyanobacteria. These are naturally occurring in ponds, lakes, and slow moving rivers throughout Ohio. During the summer, warm temperatures, and an excess of nutrients (entering the water from nearby areas after rainfall) cause the blooms as the numbers of the cyanobacteria increase.

 What do the advisories mean?

  • A Recreational Public Health Advisory means that swimming and wading are not  recommended for children, pregnant or nursing women, those with medical conditions, or pets.
  • An Elevated Recreational Public Health Advisory means toxin levels are high and all contact  with the water should be avoided.

What should I do if a HAB advisory is posted?

  • When an algal bloom is present, stay out of the water. Avoid swimming, water skiing, wading, or any other water contact.
  • If you do swim or wade, rinse off with clean water, even if no visible signs of algae are present.
  • Keep pets out of the water. If they get in the water, rinse them off immediately with clean water. Don’t let them lick their fur until they’re rinsed off.
  • Do not drink or cook with untreated lake water.
  • The toxins caused by HABs can make you sick just from skin contact. The water does not have to be swallowed to cause an illness.

What type of sickness do the algal toxins cause?

  1. Skin contact with water:

    • Rashes, hives, or skin blisters

  2. Breathing of water droplets/mist:

    • Runny nose/eyes, sore throat, asthma-like symptoms, allergic reactions

  3. Swallowing water:

    • Severe diarrhea and vomiting, abdominal pain

    • Abnormal liver or kidney function

    • Weakness, tingly fingers, numbness, dizziness


If you become sick from touching or swallowing the water contact your physician immediately

If your pet becomes sick, contact your veterinarian.

Is my drinking water safe?

  •  The HAB advisory affects surface water, not drinking water.
  • Water drawn from Harsha Lake that is used for drinking water goes through multiple treatment methods at the Bob McEwen Water Treatment Plant to make sure it is safe to drink.

Is it safe to fish in waters when an advisory is posted?

The Ohio EPA recommends to remove the fat, skin and organs, and rinse the fillets in tap water before if you plan on eating the fish you catch.

Additional Resources

Ohio Department of Health Harmful Algae Bloom webpages -

Ohio Environmental Protection Agency Harmful Algal Blooms web pages -

Ohio Department of Health Implications for tap/drinking water and recreational waters -

Up to date algae advisories

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