Harmful Algal Blooms

Harmful algal blooms are a major environmental problem in all 50 states and can be known as red tides, blue-green algae or cyanobacteria.  Harmful algal blooms have the potential to cause severe impacts on human health, aquatic ecosystems, and the economy.

It is important to understand that algal blooms have the potential to be toxic and have the ability to be injurious to your health.  Water that is green, scummy or smells bad may be experiencing an algal bloom.  It is important to keep people and pets away from water that is experiencing a known harmful algal bloom.


What causes toxicity?

Media and scientific entities believe the cause of harmful algal blooms originate from cyanobacteria that naturally occur in freshwater and marine waters.  Cyanobacteria is often confused with filamentous algae that generally does not produce toxins.  Harmful algal blooms occur when an adequate amount of oxygen, sunlight, and warm temperatures meets an excessive amount of nutrients, nitrogen and phosphorous.

Microcystis colonies seen through a microscope. Source: Dr. Hans W. Paerl, UNC-CH Institute of Marine Sciences.
Microcystis colonies seen through a microscope. Source: Dr. Hans W. Paerl, UNC-CH Institute of Marine Sciences.

Cyanotoxins naturally occur in the algae throughout their life cycle.  When cyanobacteria deplete oxygen in the water, the cyanobacteria will begin to die, their cells will rupture, and cyanotoxins are released into the surrounding water.  Cyanotoxins have the ability to affect the liver (hepatoxic), nervous system (neurotoxic), and the skin (acutely dermatoxic).  According to the United States Environmental Protection Agency (USEPA), hepatoxic freshwater blooms of cyanobacteria are more commonly found that neurotoxic blooms throughout the world.  The most commonly occurring cyanotoxins are:  microcystins, cylindrospermopsin, anatoxins, and saxitoxins.  Listed below is a table from the Ohio EPA with the threshold levels for the cyanotoxins mentioned in the previous sentence.

For a better understanding, the term micrograms per liter (µg/L) can be translated into parts per billion (ppb).  Imagine that a room is filled with one billion molecules.  It only takes one third of a molecule (1/3) to affect children under six and those with compromised immune systems.


Capture 22


Am I going to be affected by Harmful Algal Blooms?

As mentioned above, harmful algal blooms need a very specific environment to occur.  Cyanobacteria needs a food source, oxygen and a good amount of sunlight.  Harmful algal blooms have the greatest potential to affect water supplies where nutrients are actively discharging into.  Lake Erie accepts freshwater supplies from the Great Lake Erie Basin, which includes, agriculture, fossil fuels, stormwater, and wastewater.  All of those sources contribute to the active growth of cyanobacteria.

Typically, harmful algal blooms only affect surface water supplies, such as, ponds and shallow wells.  Cisterns, hauled water tanks, springs, and wells are typically not affected by harmful algae blooms.  Please click on the link if you have questions regarding harmful algal blooms and your private water system.  If you feel that your water is experiencing a harmful algal bloom and would like to have it tested, please click on the following link from the Ohio EPA for certified testing labs.

Harmful Algal Bloom Response For Recreational Waters

The most common ways that people and animals come into contact with algal bloom-contaminated water are by swallowing the water, through contact with skin during swimming or wading, or by breathing in aerosolized water droplets or spray such as when tubing or water skiing.

Depending on the type and levels of algal toxins in the water and type of contact, health effects of algal bloom exposure can range from a rash, hives, blisters, severe diarrhea, vomiting, and abdominal pain to numbness, dizziness, abnormal liver function, difficulty breathing and death. These symptoms can occur more quickly and severely in dogs and other animals.

Individuals should seek medical attention if they believe that they have been exposed to algal toxins and are having adverse health effects.  Contact a veterinarian immediately if pets and other animals have been exposed to contaminated water and show signs of illness.

Recreational Water Thresholds

Be alert for these advisories and changing water conditions.

General Signs

These signs will be posted at state park beaches and boat ramps. The white sign describes what a harmful algal bloom looks like and advises that people be on the alert and avoid them.

Recreational Public Health Watch Advisory

An orange Recreational Public Health Watch Advisory will be added to the white sign when a HAB is visually confirmed and/or when toxin levels are equal to or exceed their “watch” threshold. It indicates that an algal bloom has been detected, and that swimming and wading are not recommended for children, pregnant or nursing women, those with certain medical conditions and pets.


Recreational Public Health Warning Advisory

A red sign will be added to the white sign when HAB toxin levels are equal to or exceed their “warning” threshold. It advises that algal toxins at unsafe levels have been detected, and swimming, wading and water activities that create spray are not recommended.


Defiance County Recreational Advisory in Place:

Maumee River- Recreational Public Health Advisory

Ohio Advisories in Place:

Ohio BeachGuard