When it comes to keeping ponds, lakes, rivers and other bodies of water free of invasive weeds and algae, using the right weed killer is crucial. Applying the wrong chemicals near water can be disastrous for the local ecosystem, poisoning fish and beneficial plants. However, ignoring excessive weed and algae growth allows it to spread, using up vital resources needed by other aquatic life. The key is finding an effective weed killer that is designed to be safe for use around waterways.
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What factors make a weed killer “water safe”?
For a weed killer to be considered safe for aquatic use, it must meet certain criteria:
- Rapid breakdown – The chemicals should quickly dissipate from the water to limit exposure to fish and other wildlife.
- Low toxicity – At recommended application rates, the product should not pose significant risk to aquatic animals or plants.
- Targeted effects – The herbicide must be effective at controlling nuisance weed and algae species but gentle on desirable native plants.
- Limited persistence – The chemicals should not linger long in sediment or plant matter to avoid accumulation over time.
Herbicides that meet these qualifications are unlikely to cause lasting damage to an aquatic environment when used responsibly according to label directions.
Chemicals to avoid around water
Certain common terrestrial weed killers are ill-suited for use around water bodies:
- Glyphosate – Widely used in agriculture, this chemical is toxic to fish and may accumulate in sediments.
- 2,4-D – A possible carcinogen that is moderately toxic to aquatic life.
- Diquat – Fast-acting and non-selective, this herbicide can be extremely dangerous to fish if it enters water.
- Oryzalin – Persistent in the environment and toxic to algae, this chemical can harm pond ecosystems.
While formulations containing these herbicides are very effective at controlling weeds, their risks usually outweigh potential benefits for waterway use. Always check labels thoroughly before applying any weed killer near lakes, rivers or ponds.
Weed killers safe for use around water
The following EPA-registered weed killing products can be used safely in aquatic environments when label directions are precisely followed:
| Herbicide | Application | Target Species | Toxicity |
|---|---|---|---|
| Fluridone | Ponds, lakes, reservoirs | Submerged weeds, algae | Low toxicity to fish and wildlife |
| Glyphosate (aquatic formulations) | Ponds, lakes, along shorelines | Floating weeds, emergent weeds | Low toxicity with surfactants safe for aquatic use |
| Imazapyr | Lakes, rivers, shorelines | Broadleaf and woody weeds | Low toxicity when used according to label |
| Sodium Carbonate Peroxyhydrate | Ponds, lakes, contained sites | Algae | Low toxicity to aquatic animals |
| Penoxsulam | Ponds, lakes, reservoirs, ditches | Submerged, floating, and emergent weeds | Low toxicity to fish and wildlife |
Always consult product labeling for precise application rates and directions for your specific weed problems. Using more than recommended or applying an aquatic herbicide improperly can lead to plant and animal deaths.
Tips for safe application around water
When using weed killers near sensitive aquatic environments, follow these guidelines for best results and safety:
- Identify weeds – Correctly identifying weed species ensures you choose an effective herbicide.
- Read all labels carefully – Follow all product label instructions exactly as specified.
- Check water body restrictions – Many herbicides prohibit direct water application.
- Limit runoff – Use buffer zones between treatment area and water to catch excess chemicals.
- Avoid overuse – Stick to label application rates to minimize toxicity.
- Monitor conditions – Check for unintended plant damage or return of weeds.
- Use combination treatments – Alternate approved herbicides to curb resistance.
- Rinse sprayers thoroughly – Prevent cross contamination between chemicals.
Physical and biological weed control
While herbicides provide effective weed suppression, you can also utilize physical and biological controls to limit growth of nuisance plants:
- Physical removal – Manually uprooting, raking or hand-cutting weeds.
- Dredging – Excavating and removing bottom sediments choked with organic matter.
- Bottom barriers – Blocking light with impermeable covers to retard plant growth.
- Mechanical cutting/harvesting – Mowing or harvesting dense surface weeds.
- Water level manipulation – Raising or lowering water levels to stress unwanted plants.
- Supplemental stocking – Adding grass carp that voraciously consume vegetation.
- Beneficial microbial products – Applying pond bacteria/enzymes to digest organic sediments.
An integrated solution combining limited herbicide use with preventive physical and biological controls often provides optimal long-term aquatic weed management.
Best weed control methods for common water weeds
Managing different types of weeds and algae requires tailored control approaches using appropriate herbicide and non-chemical techniques:
Submerged weeds
- Hydrilla, Brazilian Elodea – Fluridone, Copper, Triploid Grass Carp
- Eurasian Watermilfoil – 2,4-D, Triclopyr, Mechanical Harvesting
- Curlyleaf Pondweed – Endothall, Aluminum Sulfate, Water Level Drawdown
Floating weeds
- Water Hyacinth – Glyphosate, Mechanical Shredding, Insect Biocontrols
- Water Lettuce – Copper, Diquat, Manual Removal
- Duckweed – Fluridone, Aluminum Sulfate, Biological Cleaners
Emergent weeds
- Cattails – Glyphosate (aquatic), Imazapyr, Mechanical Removal
- Phragmites – Imazapyr, Glyphosate (aquatic), Mowing
- Bulrushes – Imazamox, Penoxsulam, Repeated Cutting/Removal
Algae
- Filamentous Algae – Copper, Aluminum Sulfate, Beneficial Bacteria
- Planktonic Algae – Fluridone, Water Dyes/Surface Covers, Aeration
- Chara – Flumioxazin, Copper, Substrate Covers
Identifying the specific weed varieties in a water body allows matching them to the herbicide and control methods proven most effective.
Conclusion
Keeping waterways weed-free while protecting fragile aquatic environments requires an integrated approach. Start by selecting EPA-approved herbicides specifically formulated for water use at proper application rates. Combine periodic use of safer weed killers with preventive physical and biological controls for best results. Avoiding cross-contamination and closely monitoring conditions preserves water quality and the health of fish, plants and other aquatic organisms. With the right weed control strategy, you can safely eliminate invasive vegetation without damaging lakes, ponds and other water habitats.