Toledo, Ohio – A growing cyanobacteria bloom in western Lake Erie is prompting renewed safety warnings for boaters and swimmers this week, as shifting winds push dense algae across the Michigan and Ohio shorelines. The thickest concentrations are now in the western basin, stretching from Maumee Bay past Monroe and east toward West Sister Island.
According to the Cooperative Institute for Great Lakes Research, southerly winds have driven the bloom into open waters, while Sandusky Bay is also seeing widespread mixed cyanobacteria growth. In some scum areas there, microcystin levels may exceed the recreational safety threshold of 8 µg/L. While most open-water toxin measurements remain below that limit, experts warn scum can hold much higher concentrations, posing risks to people and pets.
Satellite data from August 11 shows the bloom’s strongest activity along the Michigan coast and near-shore Ohio waters, with orange and red zones in forecast maps signaling potential toxin hotspots. Officials advise avoiding contact with green, discolored, or scummy water, especially during calm conditions when toxins can concentrate.
Monitoring will continue through the week, with bloom movement expected as winds shift. Safety advisories remain in effect until toxin levels drop or bloom activity subsides.
