As a lake researcher, I have in recent years had quite a few people ask me whether jellyfish really do live in lakes. Some people think they are seeing things, or that their friends or family are. I’ve even heard of marital spats over the issue! So, are jellyfish present in Canadian freshwater lakes or not?

Yes, jellyfish do exist in lakes here in Canada. These organisms are related to saltwater jellyfish (Cnidaria), only much smaller. The reasons why more people are suddenly becoming aware of these creatures is simply due to their growing numbers — numbers that are on the rise due to climate change.

The bottom line is that freshwater jellyfish are real, and Canadians need to get used to their growing presence in our lakes as the planet warms.

This article is part of our series Our lakes: their secrets and challenges. The Conversation and La Conversation invite you to take a fascinating dip in our lakes. With magnifying glasses, microscopes and diving goggles, our scientists scrutinize the biodiversity of our lakes and the processes that unfold in them, and tell us about the challenges they face. Don’t miss our articles on these incredibly rich bodies of water!

Currently, the most observed genus in many parts of the world, including Canada, is Craspedacusta, with the most common species being Craspedacusta sowerbii. Some have given it the common name of Peach Blossom Jellyfish. In French it is simply known as the “méduse d'eau douce”.

This species of freshwater jellyfish was first described and scientifically named in 1880 at the Royal Botanical Gardens in London. They are an introduced........

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