Updated on Oct. 02, 2024
Tired of slimy weeds and algae taking over your favorite swimming or fishing spot? Learn about six highly effective, fish-friendly lake weed killers.
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When I was growing up in rural Northern Ontario, Canada, summer didn’t officially start until my siblings and I jumped into any one of the handful of nearby inland lakes for the first swim of the season. Healthy lakes are great for swimming, fishing, boating and summertime fun, and I prefer them infinitely to backyard pools.
And yet, natural lakes and ponds do have one major downside — weeds. Feeling slimy tendrils of green stuff brushing against your body as you swim isn’t fun, and neither is getting stringy weeds tangled in your fishing boat’s motor.
These problems are a pain, but certainly aren’t insurmountable. Aquatic weeds can be reduced significantly in two ways: with dedicated weed removal tools or herbicides.
Tools are great if you don’t mind a little exercise and only have a small area of weeds to clear. They’re also perfect for areas where local authorities frown on aquatic herbicide use. Environmentally friendly herbicides are a better choice for large areas of weed infestation, or for those lacking the time and inclination to invest much elbow grease in weed removal. If this is you, keep reading for six great aquatic weed killing products.
Note: Be sure to check with local authorities before purchasing or using any aquatic herbicide.
Approved by the Minnesota Department of Agriculture as safe for humans, fish and aquatic wildlife, this granular herbicide begins working on weeds right away, and usually kills them within a week or two.
Best applied early in the season, the product works well for removing many aquatic weed varieties, but is particularly effective at dealing with curlyleaf pondweed. It strictly follows all government safety requirements, even if the recommended dosage is exceeded.
Extremely effective as an aquatic weed killer, Aquashade Plus stands out from other herbicides because it doesn’t need to be diluted into the entire body of water or even come in contact with weeds to get rid of them.
Rather than break down the cell walls of weeds as other aquatic herbicides do, Aquashade simply blocks their access to sunlight. That prevents photosynthesis, ultimately killing surface algae and underwater plant growth.
Aquashade colors the water’s surface dark blue with environmentally friendly dye. This prevents sunlight from filtering through the water and stops weeds from growing. It’s non-toxic, safe for aquatic creatures and humans, and fast and easy to apply.
Bottom growing algae can be pretty tough to kill, and can drastically reduce the enjoyment and safety of your lake. Rocky bottomed bodies of water are particularly vulnerable to the stuff because it spreads quickly from rock to rock, making the lake bottom incredibly slippery and difficult to walk on.
That’s where Cutrine Plus algaecide comes in. The product comes in granules that sink fast, contacting slimy bottom growing algae. The copper compounds in the product chemically bind with algae cells, damaging them and halting photosynthesis.
Not only is this product fully safe for humans and animals who come in contact with the water after treatment, but the treated water can even be safely used for crop irrigation.
It stands out among aquatic herbicides for its unique effectiveness against shoreline aquatic plants with deep roots, like cattails and water lilies. It’s also effective against other weed varieties and algae.
Made with a high concentration of copper sulfate pentahydrate, Crystal Blue’s algaecide is particularly effective against thick, slimy mats of surface algae. Like other copper-based herbicides, it works by damaging plant cells, preventing photosynthesis, and thus killing the plant.
Having seen it in action, I can attest that it provides a knockout punch to most algae after only a single use. However, although it’s Environmental Protection Agency (EPA) approved as safe for human contact when used at the correct dosage, it’s too potent for small ponds or pools. And it’s not recommended for water with koi or goldfish varieties.
Another granule-based aquatic herbicide, Navigate kills lots of invasive pond and lake weeds, and continues to release weed killing agents for a long time after just one use. The heat-treated granules dissolve slowly, allowing them to work much longer than most herbicides, while leaving all fish and animal life in the water healthy and unaffected.
