Cottage Q&A: Leaf litter and the lake

Published: March 31, 2021

A green leaf floating in the lake By Eliot Holzworth/Shutterstock

This spring, we noticed a mass of leaves floating down our bay. We think our cottage neighbour might be blowing leaves into the water. Is this okay for the lake?—A pollution patroller

You’re probably worried because you know that decomposing leaves can add phosphorus to the water. And too much phosphorus is not good for a lake; it can boost the growth of algae.

But the likelihood of that, in the situation that you’re describing, is very low, says Paul Frost, a professor in the biology department at Trent University in Peterborough, Ont. Frost has conducted research on leaf breakdown and nutrient release in cottage lakes. “It comes down to the ratio of leaves in comparison to the size of the body of water,” he says. “You would need to add about 1,000 kg of leaves to increase phosphorus concentrations enough to have an effect on algal growth in quite a small lake—for example, one with a depth of 10 metres or less.” For a more typically sized cottage lake—30 to 50 metres deep—you’d need at least 100,000 kg. This is the weight of 17 elephants. Or one airplane.

This genius just reinvented the chore of raking leaves

Still: “We wouldn’t recommend that people deliberately dump leaves in the lake,” says Colleen Fennig, the general manager at the Wascana and Upper Qu’Appelle Watersheds Association Taking Responsibility in Regina, Sask. “If we’d suggest anything, it would be that people use their leaves as mulch or compost.” (Or, hey, just leave them where they fall.)

Your municipality may have bylaws about what to do with leaves or programs for collecting them. If so, you could casually bring it up with the neighbours: “Are you pumped for Yard Waste Collection this year? It’s so much better than just blowing that stuff into the lake, amirite?”

This article was originally published in the Spring 2018 issue of Cottage Life magazine.

Got a question for Cottage Q&A? Send it to answers@cottagelife.com.

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