Aquatic Weed Control

Are all aquatic plants bad?

No. Native plants provide oxygen, shelter for young fish and food for waterfowl. A pond with no plants is rarely healthy. Problems arise when one plant, especially an invasive one, crowds out everything else or covers too much of the surface.

Define what a problem means for you. If you swim, fish or water livestock, you may want some areas kept open while leaving other shoreline plant growth alone.

Some plants float on the surface, some grow up from the bottom and some remain submerged, and each group responds to different treatments, which is why identification matters so much.

How do you identify what is growing?

Treatment depends on the plant. Floating plants, submerged plants and algae need different approaches, and some plants look alike. Take clear photos and a sample in a bag, and ask your extension office or state natural resources agency to identify it.

Some aquatic plants are regulated as invasive and must be reported. Never move plants from one water body to another.

Look for signs such as thick mats, fragments floating in the water or plants sold at water garden stores. Some aquatic invaders arrive through the pet and garden trade, which is one reason not to dump aquarium contents anywhere. Take your sample to a local office in a sealed bag with some water to keep it fresh, and ask how soon they need it. Some agencies also accept photos by email.

• Photograph the whole plant and leaves
• Collect a sample for identification
• Note where and when it appeared
• Record how much of the surface it covers

What causes aquatic weed growth?

Excess nutrients from runoff, shallow water, warm temperatures and lots of sunlight all encourage plants. Fixing the cause is more lasting than treating the symptoms.

A buffer strip, reduced fertilizer use, and keeping livestock out can slow regrowth. Deepening shallow edges may help, but may require permits.

Shade from trees and plants on the shoreline can reduce the sunlight that lets weeds grow, but avoid heavy leaf fall into the water, since decay adds nutrients. Dredging or deepening edges can discourage rooted weeds but may disturb the bottom and need permits. Ask your state agency before moving soil.

What control methods are used?

Methods fall into several groups: physical removal by hand or rake, managing water levels, shading, biological controls such as certain fish in some states, and chemical treatment with approved products.

Each has trade offs and rules. Chemical treatments must follow the label exactly, and many aquatic herbicides require licensing or permits in some states. Treating too much at once can kill plants and then drain oxygen, which may kill fish.

Hand pulling and raking work for small patches, and disposal on dry land far from water prevents spreading. For larger problems, advice from a professional matters, since poor timing or dosing can cause oxygen crashes. Dyes, aeration and bacterial products are marketed for ponds, and results vary. Ask your extension office what evidence supports a product before spending money.

What rules and permits might apply?

Rules about aquatic herbicides, grass carp and other biological controls vary widely by state. Some require permits, some restrict species and some limit who may apply products.

Call your state natural resources or fish and wildlife agency before using any treatment or introducing any animal. Using the wrong product or species can be illegal and can cause real harm.

Some states also restrict stocking of grass carp or require sterile fish, and they may require a permit. Ask before purchasing, since illegal stocking can carry penalties.

How do you protect people, animals and water use?

Products carry restrictions on swimming, fishing, drinking and irrigation after treatment. Follow the label and post warnings as required. Keep children and animals away as directed.

If you use pond water for irrigation or livestock, check the label for waiting periods and ask your extension office.

A licensed applicator can help interpret labels and avoid mistakes. Ask your state agency whether you need a license for the product you are considering. Keep treatment records, including dates, product names, amounts and weather. If something goes wrong, those details help experts understand what happened.

How do you prevent weeds from coming back?

Reduce nutrient inflow, keep shoreline plants that shade water, clean boats and gear moving between waters, and inspect regularly. Early action is easier and cheaper than a full take over.

Keep notes and photos each season so you can see what is working. Consult an expert before repeating a treatment.

Be realistic. Aquatic plants are part of ponds, and some regrowth is normal. The goal is a manageable balance rather than a perfectly clear pond.

Last reviewed: November 12, 2026. Written by the Rural Farm Life Editorial Team. See our editorial policy.