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Should you be removing the weeds from your lake?

weed harvestor removing weeds from lake Photo by meunierd/Shutterstock

For most people, there’s nothing worse than diving into your lake and getting a face full of weeds. Slippery, slimy, and almost prehensile in their ability to tangle around your arms and legs, some cottagers have started using harvesters and other weed-clearing machines that seemingly clean up their waterfronts. While this may provide short-term swimming benefits, it can negatively impact your lake’s ecology and your long-term enjoyment of the lake.

“If we’re looking purely at the aquatic ecosystem—that includes all the organisms that live in the lake, even those that fly in, like waterfowl, for example—they all greatly benefit from aquatic plants,” says Andrea Kirkwood, an environmental biology professor at Ontario Tech University in Oshawa, Ont.

Lake weeds—or as they’re more affectionately known: aquatic plants—typically grow in a shallow band around a lake’s shoreline where they’re close enough to the surface to absorb sunlight.

You can think of aquatic plant beds the way we think about coral reefs in the ocean: they are integral in supporting the health and life in your lake. “About 90 per cent of biological activity in a lake occurs in the nearshore area where these plants exist,” Kirkwood says. “The plants provide habitat for little fish nurseries, so little fish can hide from predators in the weed beds, allowing them to grow. There are bacteria and microbes and little invertebrates that grow attached to the plants. And then there’s some fish that actually eat the plants, too.”

By providing necessary oxygen and shelter for organisms, these plants help stabilize a lake’s food web, all the way up to fish-eating animals, such as birds.

Cottagers who choose to alter their shoreline, by cutting down trees and clearing aquatic plants, upset the ability of the environment to maintain ecosystem health. Without plants securing the soil, the shoreline erodes during heavy rainstorms, allowing runoff to filter into the lake.

What is the best way to control weeds in swimming and boating areas?

“When you don’t have aquatic weed beds there to trap those sediments at the shoreline, all that dirty water enters the lake. In the dirt are nutrients and when there are no aquatic plants to absorb those nutrients, algae take advantage of that, and you can actually promote algal blooms,” Kirkwood says.

Algal blooms can be toxic to a lake’s ecosystem, blocking sunlight and killing off other aquatic plants. And when the algae die, the bacteria that decompose them remove oxygen from the water, killing fish in the area. Really severe algal blooms, known as blue-green algae, can even produce toxins harmful to humans.

On top of algal blooms, lakes also have to contend with invasive plants, such as the Eurasian Water-Milfoil and Starry Stonewart, which displace native plants and can actually reduce oxygen levels in the lake from decomposing plants. But trying to clear these weeds, especially with a harvester, exacerbates their spread. 

“Some research from the United States has indicated that when people use mechanical harvesters, they end up breaking the plants into bits and pieces. Most of the biomass is removed, but there are always going to be little stragglers that are left behind. Those stragglers can turn into whole plants relatively quickly, just from vegetative growth,” Kirkwood says. “It’s likely that using mechanical harvesters help it spread and grow in more places.”

Instead of mechanical harvesters, Kirkwood says she has heard of people trying to remove the plants by hand, using a snorkel and collecting them in a net. “It’s just very labour intensive,” she says. “But at least it’s acknowledging that mechanical harvesting is the worst thing you can do.” Here’s what you need to know to remove invasive plants safely and legally. However if you do see them, Ontario’s invading species program asks you to contact the Invading Species Hotline at 1-800-563-7711, visit EDDMapS Ontario, or search for the Invasive Species in Ontario project on iNaturalist.org to report a sighting.

Kirkwood’s suggestion is that people need to start learning how to live with aquatic plants. “Rather than trying to mow down and remove all the weeds in front of their property, what about just a small area where they can harvest and leave the rest to the animals and organisms that live in the lake,” she says. One important function of plants is to fight erosion. Here are some plant options you can use to stabilize your shoreline naturally.

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