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A jellyfish has been discovered in a central Wisconsin lake, but swimmers don't need to worry, since the creature is about as big as a penny.

The freshwater jellyfish was discovered in Spencer Lake in Waupaca County last week, making it the 94th body of water in Wisconsin known to contain jellyfish.

In Madison, Lake Mendota and the duck pond at Wingra Marsh harbor jellyfish, and jellyfish have been found in Fox Lake in Dodge County, Big Green Lake in Green Lake County and Devil's Lake and Skillet Creek Farm Pond in Sauk County, according to the Wisconsin Department of Natural Resources.

The list of lakes and ponds containing jellyfish can be found here.

The creatures are harmless to humans, said Paul Skawinski, an invasive species specialist, in a news release from the Golden Sands Resource Conservation and Development Council in Stevens Point.

"Their stinging cells are only effective against small creatures like plankton," Skawinski said. "They are too small to pierce human skin, so they pose no threat to swimmers or other lake users."

The freshwater jellyfish originally came from China and were first seen in Wisconsin in the 1960s, most likely coming in on aquatic plants imported for aquariums or water gardens, then getting into lakes during flooding or by aquarium water being dumped.

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