What is the best way to deal with weeds in swimming and boating areas?
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. Cottagers should minimize phosphorus runoff by forgoing fertilizers and maintaining a shoreline buffer.
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 municipality office for specifics.
If you choose to physically remove plants, work permits that specify the method, maximum area, and timing of weeding will be needed. If ministry specialists are familiar with the lake, a site visit may not be required. Removal can only be done after fish spawn.
Generally, plants should be removed by hand, but tools, including specialized rakes, cutter bars, which are dragged over the lakebed to sever plants, or weed mowers, which rip and tear vegetation, may also be allowed. Hand pulling and cutter bars are effective in removing plants from small areas near shore. To ensure vegetation doesn’t spread avoid 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, they can kill all life not just aquatic plants.
Herbicide use is illegal in some parts of Canada without a permit from the Ministry of the Environment (MOE) or Parks Canada. If you believe herbicides are necessary, 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
A herbicide permit will spell out all conditions of use, from the timing, type, and amount of herbicide to the size of the treatment area. 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, and it is advisable to start the permit process in winter or early spring to ensure approval in time for the usage period the ministry mandates. Regardless of the removal method used, you’ll have to reapply for a permit each year.
