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Harmful algal bloom season starts early, two webinars slated

Appearing earlier than usual, a harmful algal bloom (HAB) on Lake Cadillac was verified by the Michigan Department of Environment, Great Lakes, and Energy (EGLE) staff after they spotted it last week. They collected samples near the lake’s boat launch and the beach. The results were positive for microcystin, a toxin released by some types of cyanobacteria, often referred to as “blue-green algae”.

A Harmful Algal Bloom on Lake Cadillac in June 2023.

Harmful algal bloom on Lake Cadillac in June 2023.


The term HAB generally describes accumulations of cyanobacteria in amounts that are aesthetically unappealing and capable of producing toxins. While not all cyanobacteria produce toxins, significant blooms can still pose risks to human and ecosystem health.

It is not possible to determine whether algal blooms contain harmful toxins by looking at them, so it is best to avoid contact with blooms or significant surface scums.

Summer is peak season for the formation of HABs that can present health hazards to people and pets.

In general, blooms develop when:

  • High amounts of nutrients are in the water.
  • Surface water conditions are calm.
  • Water temperatures are high.
  • Zebra or quagga mussels are present in low nutrient lakes.

“While blooms sometimes do occur earlier in the spring, most of the blooms we respond to occur later in the summer,” noted Donal Brady, an environmental engineer in the Water Resources Division in EGLE’s Cadillac District Office. “Some blooms occur at surprising times, and it was surprising to see this bloom.”

Two free webinars on HABs are scheduled soon:

  • The Ohio Sea Grant will host a free public webinar from 11 a.m. to 1 p.m. on June 29 that will focus on the seasonal forecast for HABs for Lake Erie this year. Registration is now open.


  • Harmful Algal Blooms in Michigan’s Recreational Waters is a webinar hosted by EGLE and the Michigan Department of Health and Human Services (DHHS). It is scheduled from 1 p.m. to 2 p.m. on July 13. Registration is now open.

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 Photographs are very helpful.

Reports of cyanobacterial blooms and results of cyanotoxin testing in Michigan can now be found online at the Michigan Harmful Algal Bloom Reports map. The Michigan Harmful Algal Bloom Reports map was developed by MDHHS, in collaboration with EGLE and other stakeholders, to share available information about HABs. The Michigan Harmful Algal Bloom Reports map will be updated once per week during June through November and 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.

More information about cyanobacterial blooms can be found on the EGLE HABs website which has a link to a helpful photo guide.