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BRYOZOANS:  A naturally occurring phenomenon

A bryozoan lifted out of the water by the stem of the aquatic plant attached to it
Environment, Great Lakes, and Energy

BRYOZOANS:  A naturally occurring phenomenon

The Michigan Department of Environment, Great Lakes, and Energy (EGLE) often receives complaints claiming that there are gelatinous balls, floating blobs and even “water boogers” some as large as basketballs on the lake shore or in a lake or pond. This phenomenon is due to the presence of bryozoans, also called moss animals, which are not a sign of pollution.

several bryozoan colonies under water with the sun shining through the water onto them.

Colonies of freshwater bryozoans form gelatinous ball-like masses and are commonly found in small farm ponds in water less than a meter in depth and in shallow eutrophic (nutrient enriched) lakes and open areas of swamps for brief periods. They have also been reported to wash up on shores of deep inland lakes after storms. The colonies commonly attached to rocks, underwater branches, or even boats. They grow throughout the warm season reaching their largest size in the fall then dying in the winter.

close-up of a bryozoan colony

Bryozoans are water animals that live in colonies made up of microscopically connected individuals called zooids. Bryozoans are invertebrates (animals without backbones) that have a box-like or tube-shaped body, a U-shaped gut, and a cluster of tentacles to trap small particles of food. Worldwide, there are about 5,000 species of bryozoans. While most are marine species, some are freshwater.

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For more information, including tips to help reduce the amount of nutrients that can enter a lake from your home activities, contact any EGLE district office or call the State of Michigan’s Environmental Assistance Center at or 800-662-9278.

If you find pollution and believe it is human-induced, please report it to the State of Michigan’s Pollution Emergency Alerting System (PEAS) hotline at (800) 292-4706.