If it looks like a jellyfish, swims like a jellyfish, and quacks like a jellyfish, then it probably is a jellyfish.
Hold on. Jellyfish don’t quack. I think I got that saying mixed up with the one about the duck. My point is, freshwater jellyfish do exist. They’re actually quite common and can be found in most lakes and streams in Michigan.
So, technically, they’re not true jellyfish. But they’re close. Freshwater jellyfish (Craspedacusta sowerbyi) are related to marine species of jellyfish, but they have a membrane called a velum that the marine species do not have.
Despite their differences, they look like and move like true jellyfish.
They have been spotted throughout most of North America for more than a century and it is believed they came from Asia. They are not harmful to humans and environmental officials believe they have negligible adverse effects on the aquatic environment.
“Though freshwater jellyfish do have stinging cells like the marine species, their tiny size means they lack the ability to sting, and so they’re not harmful to people. It is also believed to be unlikely that freshwater jellyfish could consume enough zooplankton in our bodies of water to negatively compete with fish species,” Tim Cwalinski, the DNR’s northern Lake Huron manager said.
Where are freshwater jellyfish found in Michigan?
The first reports of freshwater jellyfish in Michigan came from the Huron River in 1933.
Now they’re found in most lakes and streams. Late summer and early fall is the best time to catch a glimpse of these elusive invertebrates.
This is because of the lifecycle of the jellyfish. They spend winter in a podocyst resting stage. In the spring, the podocysts develop into polyps and continue the life cycle with asexual reproduction.
By late summer, the polyps develop into the medusa stage. This is when they most appear like what people picture when they think of jellyfish. They can range in size from a penny to a quarter.
“If you’re among those to observe a single medusa stage or colony of freshwater jellyfish this year in our lakes or slow-moving streams, consider yourself fortunate, don’t panic, and understand this is simply an invertebrate that has inhabited most of our waterways for a century,” Cwalinski said.
The Great Lakes Environmental Research Laboratory offers a list of sightings online.
Map shows locations where freshwater jellyfish were reported
---> Can’t see the map? Click here.