Last summer, our grandson, while kayaking, noticed the lake water foaming. It was followed by bubbling that can be compared to the effervescence from an open soda can. Can you explain this to us?–Peter and Nicole Porteous, Sharbot Lake, Ont.
We can try. At CL HQ, we’re no strangers to questions about foamy lake water. It can look as though—gasp!—someone’s been bathing in the lake. But soap-like bubbles can happen naturally if there is a lot of decomposing organic material in the water, says Paul Frost, a biology professor at Trent University in Peterborough, Ont. “When the material aerates, like when waves are hitting the shore, this can produce lots of foam.” But the bubbles your grandson described sound different, he says.
Turns out, bubbles can appear on a lake for lots of reasons. Certain lakes release gas—it’s from flatulent fish. Oh, JK. It’s mostly from boring stuff, for example, sediment. Sometimes, “if the bottom of the lake is disturbed, that can release a bunch of built-up gases,” says Frost. “Otherwise, sometimes water turbulence, from wind, can expose bottom waters to the lake surface, and that releases a lot of gas.” He’s only seen this once or twice, and never on Ontario lakes.
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It’s also possible that a “benthic mat” of algae, after drifting to the surface of the lake, is producing gas and causing the bubbles, says Jason Venkiteswaran, a biogeochemist at Wilfred Laurier University in Waterloo, Ont. “Imagine that a layer on the lake bottom, like a carpet, has detached and floated up.” Of course, your grandson didn’t describe any algae (and algae is something that people notice).
Is your lake water especially dark? That could mean that there’s a lot of dissolved organic carbon in the water, says Venkiteswaran. “Sometimes, this can cause a film to form on the water surface and that can hold bubbles.”
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Sorry. There’s a lot of “sometimes” and “possible” in this answer. But that’s because without witnessing the bubble event, and knowing more about the makeup of your lake, it’s hard for our experts to solve this frothy mystery. Happily, there’s no reason to worry, says Venkiteswaran. “Bubbles on their own are not an indication that there’s anything wrong with a lake.”
Got a question for Cottage Q&A? Send it to answers@cottagelife.com.
This article was originally published in the June/July 2025 issue of Cottage Life.
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