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Harmful Algal Blooms

Lake Erie - green Algae
Environment, Great Lakes, and Energy

Harmful Algal Blooms


Gary Kohlhepp

Michigan's Department of Environment, Great Lakes, and Energy (EGLE) staff discover or receive reports from lake associations, and the broader public each year about nuisance algal conditions.  The number of such reports, particularly the occurrence of cyanobacteria or blue-green algae blooms and concern over the possible presence of algal toxins such as microcystin, appear to have increased in recent years.  In particular, severe blooms were observed in the western basin of Lake Erie in August 2014, and access to drinking water for hundreds of thousands of people was temporarily interrupted due to elevated levels of an algal toxin associated with the bloom.  This event caused EGLE to re-examine and expedite our efforts related to blue-green algae blooms, including what constitutes a harmful algal bloom (HAB); our monitoring approach; sampling protocols; analytical capabilities and costs; information gaps; and communication with other agencies, stakeholders, and the public on this issue. 

Summer is peak season for the formation of harmful algal blooms (HABs) that can present health hazards to people and pets. In Michigan, algal blooms typically occur during periods of warm temperatures, lots of sun, and high nutrient levels.

It is not possible to determine whether algal blooms contain harmful toxins by looking at them, so it is best to avoid contact with any body of water that is covered with algal mats or significant rafts of algae on the surface.

EGLE and the Michigan Department of Health and Human Services (MDHHS) sample for HABs on a limited basis and work with local health departments to protect the public when toxins are discovered; however, some areas affected by HABs may go undetected. Suspicious-looking algae can be reported to EGLE by calling the Environmental Assistance Center at 1-800-662-9278 or sending an e-mail to

Preview of the interactive harmful algal blooms storymap
Preview of the interactive harmful algal blooms storymap

Michigan harmful algal bloom reports web map

This map shows locations of bloom reports that have been verified by EGLE and results of any cyanotoxin tests conducted by EGLE, MDHHS, and partner agencies.

Note that not all HABs in Michigan are reported to EGLE and so may not be included on the map. HABs can move around, disappear and reappear – meaning that HABs may be present in waterbodies, but not present on the map. Before going in any water, MDHHS recommends that you always look for and keep away from visible HABs or scums and that people and pets stay out of water in affected areas.

Preview of the Harmful Algal blooms interactive story map
Preview of the Harmful Algal blooms interactive story map

Harmful algal blooms story map

 This story map covers all that and more including how to prevent and report blooms if you suspect there may be one on a waterbody in Michigan.