QUESTION

What is the best way to deal with weeds in our swimming area, if leaving them be is not an option? My family agrees that the weeds are annoying, a little bit “icky,” and need to go. Does that make us bad cottagers? 

Andrew Sjogren, Toronto, Ont.

ANSWER

Bad? No. Misguided? Maybe. While the excessive growth of aquatic plants is often fuelled by phosphorus runoff from fertilizers and septic systems, “weeds” remain an important part of your lake’s ecosystem no matter how they got there. Plants improve water quality by reducing sediment and absorbing pollutants, and provide critical habitat for birds, frogs, and fish. That’s why Fisheries and Oceans Canada (DFO) prohibits anyone from altering, disrupting, or destroying that habitat unless authorized. 

Colin Higgins, acting senior integrated resource management technical specialist at the Bancroft office of the Ontario Ministry of Natural Resources (MNR), encourages cottagers to minimize phosphorus runoff by forgoing fertilizers and maintaining a shoreline buffer. But if you just can’t live with weeds, there are options.

All of the weed control methods described below can be effective in controlling plants, but vary in their impact on the environment. With few exceptions, cottagers will require a permit from one or more government departments or agencies. Call your local MNR office for specifics.

If you choose to physically remove plants, MNR work permits specify the method, maximum area, and timing of weeding. If ministry specialists are familiar with your lake, a site visit may not be required. Removal can only be done after fish spawn – often following Canada Day – and although the maximum clearance area varies by permit, Higgins encourages cottagers to clear only what they need for swimming and boating and not to exceed a 10-metre by 10-metre area.

The MNR will generally want you to remove the plants by hand, but may also allow tools, including specialized rakes, cutter bars, which are dragged over the lakebed to sever plants, or weed mowers, which rip and tear vegetation. Hand pulling and cutter bars are effective in removing plants from small areas near shore. Ensure you don’t spread vegetation by trailing cut roots or seeds to other parts of the lakebed.

Weed mats are dark plastic or silicone rubber barriers that, when weighted to the lake bottom, cut plants off from nutrients and sunlight. Although they are effective, particularly in containing initial outbreaks of weeds, Higgins notes the MNR is unlikely to agree to them as a method of control because they “totally obliterate all life, not just aquatic plants.”

Using herbicides such as Reward, with its active ingredient diquat (and a skull-and-crossbones warning), to control aquatic weeds is illegal in Ontario unless you have a permit from the Ministry of the Environment (MOE), or Parks Canada if your cottage is on the Rideau Canal or Trent-Severn Waterway. If you believe herbicides are necessary, Violet van Wassenaer, a pesticide regulatory scientist at the MOE, recommends that you contact a ministry pesticide specialist who will assess your case and help with the permit process. Herbicides can be particularly effective in controlling some plants, such as Eurasian watermilfoil, but won’t work on others, such as tape grass.

Your herbicides permit will spell out all conditions of use, from the timing, type, and amount of herbicide to the size of the treatment area – usually a maximum of eight to 15 metres wide and up to 30 metres offshore. While the MOE does issue permits allowing cottagers to apply herbicides themselves, it recommends hiring a licensed exterminator. Aquatic plants can only be treated once the critical period for fish-spawning is over. Van Wassenaer advises starting the permit process in winter or early spring to ensure you get approval in time for the usage period the ministry mandates.

Regardless of which removal method you use, you’ll have to reapply for a permit each year. “Removing aquatic plants is a very short-term solution,” says Higgins. “When people buy a cottage and there are weeds, they should realize it’s really impossible to eradicate them.”  

Steve Brearton

Published in the June 2007 issue of Cottage Life.