Microcystis in Southwest Michigan Lakes

Dean Solomon
District Extension Natural Resources Agent
W.K. Kellogg Biological Station

Residents on some southwest Michigan inland lakes are noticing unusual blooms of a yellowish-green "scum" floating on the water surface during summer. This "scum" is a type of blue-green algae called microcystis. There are concerns that this type of algae can produce toxins potentially harmful to wildlife and people.

What is microcystis?

Microcystis is actually a type of bacteria called cyanobacteria that naturally occurs in most lakes at low concentrations. This organism forms small colonies that look like floating yellowish-green pollen or sand grains. At high populations, wind can push the colonies toward shore, forming a very dense blanket. There may also be large amounts of surface foam associated with these dense areas.

Why are we seeing more?

Although microcystis is present in most lakes, it is rarely noticeable. In recent years, though, some lakes have experienced much higher than normal concentrations.

There is much speculation in the scientific community about why this is occurring, but one of the suspected culprits is invasion by zebra mussels, a non-native pest that was introduced to the Great Lakes region in the early 1980s. These thumbnail-size mussels filter and digest large quantities of algae, but appear to "spit out" microcystis. With competing algae reduced, microcystis may build to greater concentrations than normal.

The presence of zebra mussels alone does not guarantee microcystis problems. Many other factors may contribute to the problem, including the lake's nutrient status, temperature and climatic conditions.

Researchers in Michigan, Ohio and other states are currently studying the effects of zebra mussel infestation in the Great Lakes and inland lakes, including the relationship between this pest and microcystis blooms.

Microcystis and toxicity

Microcystis can produce natural toxins, called microcystins, which can be harmful to wildlife and humans. Studies indicate that the toxin can kill wildlife if a sufficient quantity is ingested, and can cause liver damage in animals if smaller quantities are eaten over a long period of time. The effects on humans are not known, however there are some reports of individuals developing gastrointestinal distress after exposure to dense accumulations of microcystis.

Even though microcystis is common in southwest Michigan lakes, it normally does not pose any health risk to humans, pets or wildlife. Only when unusually large blooms occur does the potential exist for enough toxin to be produced to cause a problem. Microcystis blooms may or may not produce toxin. When the bloom dies off and dissipates, toxin levels in the water decline over days or weeks.

Water testing is the only way to determine whether microcystins are present. The laboratory techniques needed to perform this analysis are complicated and expensive and few labs are equipped to test for this toxin.

Risk is greatest when algal blooms are thickest, and for those who are most likely to ingest lake water (i.e. children and pets). Even so, there have never been any reports of individuals in Southwest Michigan becoming ill from exposure to microcystis.

Where to go for help

Additional information about microcystis - Contact Michigan Sea Grant Extension office (517-353-9568) or MSU's Kellogg Biological Station (616-671-2412 or 800-521-2619).

Microcystis identification - The Michigan State University Plant Diagnostic Clinic can identify microcystis (but not the presence of toxin) from algae samples in water. Contact your local MSU Extension office or the lab directly (517-353-9430). There is a fee for this service.

Health concerns associated with microcystis - Contact your local health department or Michigan Department of Community Health Toxics and Health Hotline (800-648-6942).

Links to other information

That bloomin' Microcystis: Where'd it come from? Where'd it go? - Informative article about microcystis blooms in Lake Erie. From Ohio Sea Grant.

Hazards from Microcystis in Fresh Water - Fact sheet about microcystis toxicity. From the Oregon Health Division.

Zebra Mussels, Blue-Green Algal Blooms and Other Water Quality Problems in the Great Lakes - Excellent fact sheet about microcystis including color photographs. From the Great Lakes Environmental Research Laboratory.

This information is for educational purposes only. References to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned. This information becomes public property upon publication and may be printed verbatim with credit to MSU Extension. Reprinting cannot be used to endorse or advertise a commercial product or company.

August, 1998  
updated 07/01/02