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Jellyfish believed to be a freshwater species known as Craspedacusta sowerbyi were found in a Manitoba lake. ((Bev and Harley Alexiuk))

A Winnipeg family got a bit of a surprise when they jumped into a Manitoba lake and found themselves surrounded by dozens of tiny jellyfish.

Bev Alexiuk and her family were at Star Lake, in Whiteshell Provincial Park along the province's eastern boundary, on Aug. 21 when they noticed a bloom of small translucent jellies with wavering tentacles just under the surface of the water.

'In about 45 years of sampling here in Manitoba, I've never come across it here.'—Biologist Eva Pip

Her daughter scooped up a few of them before Alexiuk could stop her. Alexiuk was afraid her daughter might get stung, but nothing happened.

Alexiuk and her family collected some of the jellies in a jar. A retired biologist confirmed them as the freshwater species known as Craspedacusta sowerbyi, she said.

"It's interesting [but] … also scary," said Alexiuk. "Unless you touched them or saw them there, it is hard to believe."

Her daughter tried to keep them in a jar, feeding them fish food, but they didn't survive.

'Red flag'

Although its origin is in China, Craspedacusta sowerbyi can now be found across the globe. It is present on almost every continent and in many U.S. states and across Eastern Canada.

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Manitoba Water Stewardship is investigating the jellyfish found at Star Lake and how they got there. ((Bev and Harley Alexiuk))

However, "in about 45 years of sampling here in Manitoba, I've never come across it here," said University of Winnipeg biologist Eva Pip. She called the discovery a "red flag" for the environment.

"It shows how disrupted the ecosystems are now everywhere, and especially freshwater," Pip said.

Manitoba Water Stewardship hasn't confirmed that the Alexiuks' find is indeed the Craspedacusta sowerbyi jellyfish. The department is looking into it.

While some jellyfish have potent venom, they are larger and found in salt water. Stings from those species are extremely painful and fatal to prey animals; some can seriously harm or kill humans.

Freshwater species are much smaller and colourless. Craspedacusta sowerbyi, about 2.5 centimetres in diameter, stings only its prey: plankton and small fish.

With files from the CBC's Leslie McLaren and Marianne Klowak