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What is blue-green algae, and why is it a problem?

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Blue-green algae

Blue-green algae has taken over the water near an Owasco Lake shoreline.

Blue-green algae, also known as cyanobacteria, is a filmy, paint-like scum that has been discovered on many water bodies across the country in recent years. Combinations of warm water and higher levels of nutrients, including nitrogen and phosphorous, allow the algae to proliferate.

Sometimes the algae contains toxins, called microcystins. Toxic blooms are known as harmful algal blooms, or HABs, and can cause health problems in humans and animals. According to the Cayuga County Health Department, contact with blue-green algae toxins can cause irritation of the skin, eyes, nose and throat and inflammation of the respiratory tract. Consuming the toxins can cause damage to the liver, kidneys and nervous system. 

The health department said people should avoid swimming and recreating in water that is discolored or filmy in appearance. It also said people should never drink, prepare food, cook or make ice with untreated surface water.

The U.S. Environmental Protection Agency released a drinking water health advisory for cyanobacteria toxins in 2015. It said for children under the age of 6, safe levels for short-term exposure are at or below .3 micrograms per liter. For children and adults over the age of 6, the advisory level is at or below 1.6 micrograms per liter.

Animals or people experiencing symptoms such as diarrhea, nausea, vomiting, irritation of the skin, eyes, or respiratory system after being exposed to a suspected or confirmed bloom should see a doctor or veterinarian. 

Anyone who suspects they've seen a harmful algal bloom should report it to or Blooms on Owasco Lake should be reported to the Owasco Lake Watershed Inspection Program at (315) 427-5188 or (315) 237-2066.

Those with concerns may contact the Cayuga County Environmental Health Division at (315) 253-1560 or visit


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