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Spot a jellyfish in Michigan? No problem, state says

Freshwater jellyfish in North America range from the size of a penny to a quarter.
Michigan Department of Natural Resources
Freshwater jellyfish in North America range from the size of a penny to a quarter.

If you think you’ve spotted a jellyfish in a river or lake, there's a chance you have. Freshwater jellyfish are pretty rare to see in Michigan, but jellyfish are most often spotted this time of year.

Freshwater jellyfish were first reported in Michigan waterbodies a century ago. Although they aren’t native to North America, the state said they pose no threat to people or the environment.

Tim Cwalinski is with the fisheries unit at the Michigan Department of Natural Resources. He said the DNR gets concerned calls from residents in the later summer and fall when jellyfish are most visible in their "medusa" stage.

“There’s a whole aquatic community out there in the water, other than the things we think of like fish, mussels, clams — and these critters," Cwalinski said. "But they’re all normal.”

Cwalinski said the transparent freshwater jellyfish are no bigger than a quarter and don’t sting. Since they lack a membrane called a velum, they're not considered "true jellyfish."

The species was first documented in Michigan in the Huron River in 1933, and it's believed they were accidentally transported from Yangtze River in China after hitching a ride on ornamental aquatic plants.

"They're an invasive from far well before our time, but I think they’re just kind of incorporated in our waterbodies," Cwalinski said. "We have species that are not native that we’ve grown accustomed to enjoying.”

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