Since the late 1990s, Lake Erie has been plagued with blooms of toxic algae that turn its waters a bright blue-green. These harmful algae blooms are made up of Cyanobacteria that produce the liver toxin Microcystin. The blooms have led to public warnings to avoid water contact, and entire community water supplies can be shut down.
This year’s bloom is expected to measure 7.5 on the severity index, but could range between 6 and 9. An index above 5 indicates blooms having greater impact. The severity index is based on bloom's biomass – the amount of algae – over a sustained period.
"Algae blooms can be a mixture of toxic and non-toxic forms, and different species of Microcystin-producing Cyanobacteria can inhabit different parts of Lake Erie," says George Bullerjahn, director of the Great Lakes Center for Fresh Waters and Human Health.
In late summer, Cyanobacteria called Microcystis are found in Lake Erie's open waters. From spring through fall, another Cyanobacteria genus, Planktothrix, blooms closer to shore. Nutrients that fuel Cyanobacteria blooms usually come from the nitrogen in agricultural runoff; the runoff makes its way into streams and rivers, eventually flowing into large waterbodies such as lakes.
Areas near shore are prone to nitrogen loss as summer progresses and the amount of rainfall - and runoff - decreases. Nutrients from spring rains spark Planktothrix blooms, but their persistence through late fall is due to the ability of the Planktothrix Cyanobacteria to "scavenge" nitrogen from their environment better than Microcystis can.
Nitrogen seems to be the common driver for toxic blooms of Planktothrix not only in Lake Erie, but worldwide. The size of a bloom isn’t necessarily an indication of how toxic it is. For example, the toxins in a large bloom may not be as concentrated as in a smaller bloom. Each algal bloom is unique in terms of size, toxicity, and ultimately its impact to local communities.
Harmful algal blooms (HABs) of Cyanobacteria (blue-green algae) in Lake Erie can produce toxins that can pose a risk to drinking water, cause skin irritation, and negatively affect wildlife, companion animals and livestock.
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Drinking Water
Health officials conduct routine monitoring to ensure that public drinking water is safe.
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Recreational Water Safely
You can still boat and recreate in Lake Erie waters, but be aware that HABs may be present.
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