How To Kill Pond Weeds

An overabundance of unwelcome aquatic plants in your lake or pond can harm the wildlife as they disrupt the delicate balance of nutrients and oxygen in the water body. Because of poor aquatic weed control, many things can be hampered, such as fishing, water sports, boating, and swimming

Weeds develop in and around ponds and lakes, like in your yard. Some weeds are beneficial, feeding fish and filtering water, but others can be problematic. Pond weeds come in three varieties, each with its own set of issues.

Submerged weeds are where only a small portion of the weed and root system is visible above water. The most common are submerged weeds such as American pond weed, bladderwort, clasping leaf, curly-leaf pondweed, and parrots feather. Emergent weeds grow near the coastline and are rooted and robust with stiff stems. Weeds of these types include alligator weed and other weeds. (Learn How To Drag Weeds Out Of Pond)

Guide To Kill Pond Weeds

You’ll find floating weeds near shallow water surface, with leaves visible above the water and have roots that may reach the pond bottom.

Floating weeds, like algae, prevent sunlight and oxygen from reaching fish. Water hyacinth, water lettuce, water shield, and water meal are common types of floating weeds.

All weeds need a specific means of pond weed control, so in this guide, you can learn how to kill weeds in a pond.

By the end, you’ll know enough about how to get rid of pond weeds and provide a good habitat for wildlife or for water activities.

How to Kill Weeds and Algae Kae Or Pond

With pond weeds, control methods can vary based on the type of weeds you have, and if you have a small pond or large lake water area, you carry out many recreational activities.

Here are some ways you can go about how to control weeds.

Pond scum and filamentous algae have similar names. These algae resemble wet wool and float on top of the water.

Planktonic algae are often known as green water algae because of their green tint. Because planktonic algae die quickly, oxygen levels in the entire pond water drop, potentially killing fish, and multiple treatments over weeks are required.

  • Some treatment products make the water unsuitable for swimming.
  • Some treatment products make fish unfit to consume.
  • Some products are harmful to aquatic wildlife and fish through oxygen depletion.
  • Some products are made for large bodies of water, while others are for a small pond.

Read Product labels before adding anything to your water, as you can quickly kill fish without realizing it. Product labels will also state if you need to wear protective clothing, such as goggles, gloves, face masks, etc.

Treating Weeds

Select a weed-specific product after recognizing the weed. Aquatic herbicides can be applied in two ways, depending on the treated weed.

They perform best on shallow or emergent weeds. Liquid herbicides are sprayed with water as directed on the product label. Weeds are immediately sprayed. Only live weeds should be treated.

Granular herbicides perform well on submerged weeds and in deep ponds. Granular herbicides are applied directly to weeds with a hand spreader, following the label’s application rate.

Treat only 1/3 of the pond or lake at a time, as dead vegetation reduces oxygen levels, harming fish and wildlife. Treat every 10-14 days. (Read Do Plants Grow At Night)

Treating Algae

After determining the type of algae, treatment can be found in liquid and granular applications.

Liquid algaecides work well on planktonic and filamentous algae, where the liquid algaecide is mixed with water and sprayed directly on algae.

The best way to treat chara algae is with granular algaecides, where the granules sink and scatter uniformly across the pond floor.

During treatment, the pond or lake water should be above 60°F. To ensure fish have enough oxygen, treat only 1/3 of the water at a time and wait 10-14 days between treatments.

Get rid of pond weeds with Herbicides

Herbicides To Control Weeds

Before looking at natural methods of how to get rid of small quantities of aquatic plants, here are some of the herbicide options to deal with many submerged plants and algae.

Copper Compounds

Because of its availability and inexpensive cost, copper sulfate, also known as “blue stone,” is one of the most widely used algae treatments.

In hard water, copper sulfate is difficult to use because it binds to calcium, precipitates out of solution, and renders copper ineffective as an algaecide.

Copper compounds can be toxic to fish if used at rates higher than those recommended on the label, and they can also be toxic in soft or acidic waters when used at recommended rates.

Before employing copper, evaluate the pond water’s alkalinity and tailor copper treatments to the alkalinity levels.


Fluridone is a systemic herbicide with a broad spectrum. Herbicides that are applied systemically are absorbed by the plant and transported to the site of action. Therefore, systemic herbicides take longer to work than herbicides that work locally.


Imazamox is a systemic herbicide with a broad spectrum. Systemic herbicides are absorbed by the plant and travel to the site of action. Herbicides that act systemically take longer to work than herbicides that act locally. To apply, an aquatically certified surfactant is required to release surface tension.


Flumioxazin is a granule that can be sprayed or injected after mixed with water. It’s a contact herbicide with a broad spectrum. Contact herbicides are pretty effective.

Flumioxazin needs to be applied to developing plants. If the herbicide is administered to the foliage of floating or emergent plants, a surfactant will be required to cut through water tension. Flumioxazin deteriorates and loses potency if the pH of the water is less than 8.5.


Bispyribac-sodium is packaged as a water-soluble powder. Each packet should first be blended with water before spraying or injecting. It’s a systemic, selective herbicide.

Herbicides that are systemic are absorbed by the plant and travel to the site of action.

Systemic herbicides are slower working than herbicides that act locally. A surfactant will be required if the herbicide is administered to the leaves of floating or emergent plants.

How To Get Rid of Aquatic Weeds?

This section is a general guide on aquatic weed control. You can control any water weed species with the aquatic herbicides provided.

Aquatic weeds thrive in lakes, ponds, and other bodies of water with aquatic fauna.

Natural filtration, food, and habitat for fish are all provided by aquatic weeds, although issues emerge when they grow too quickly.

Most aquatic weeds, such as cattails, hydrilla, and algae, are innocuous, although they can obstruct recreational activities like swimming and fishing.

Weed Control Practices

Grass carp can seldom control aquatic weeds during the first year they are stocked. Grass carp stocking rates you need to control pondweed fall between 7 to 15 per surface acre.

Only certain grass carp can be legal in certain areas, and you may need a permit to stock such fish. However, once established, triploid grass carp can be a great way to naturally deal with many pond weeds.

  • Weeds die off in warmer temperatures, reducing the amount of oxygen available in the pond. To guarantee that your fish have an oxygen-rich environment, treat your pond in tiny portions and wait for 10 to 14 days between treatments.
  • We recommend using an indicator dye with your herbicide to denote where you’ve applied it to avoid overtreating.
  • It’s vital to remember that aquatic herbicides kill the plant; they don’t treat the root cause of the weed’s growth.
  • The major reasons aquatic weeds thrive include excessive nutrients and organic waste.
  • Aquatic herbicides are a helpful tool, but they don’t solve the problem of excess nutrients and organic matter.

Following up with proactive pond management measures like aeration and natural water treatments will help maintain your water clear of pondweeds for years.

Eliminate weeds by Mechanical and Manual

Mechanical and Manual Control

American Pondweed can be eliminated from your pond by cutting and raking, although it will sprout from the remaining roots and seeds.

Pond Dye will limit sunlight entering your pond, so photosynthesis cannot function, thus resulting in stunted growth.

String algae is more manageable. Many pond owners cut, rake, vacuum, or pluck algae and lake weeds by hand because certain species look more like plants than regular algae.

String algae resembles strings, and they frequently cluster and intertwine to form mats. If the dense mats aren’t too heavy or broad, you can easily remove them using a rake or your hands.

Submerged weeds can also be removed by hand, thanks to their soft stems.

Drain Water

If manual or chemical control approaches haven’t successfully eradicated or controlled green water algae and lake weeds, your best choice is to drain, clean, and refill your pond with fresh water. (Learn How Fast Does Weed Killer Work)

The vast majority of aquatic weed species will be removed, although you’ll need to consider any fish or aquatic wildlife you have.

Chemical Control

There are several options to control American Pondweed.
Use a season-long herbicide to treat the entire body of water for American Pondweed and many other common pond weeds.

Use a broad-spectrum contact herbicide will quickly kill American Pondweed. Multiple treatments may be required during the season because it does not stay in the water body or act with rushing water.

Use such compounds as a fast way to control tough invasive and nuisance aquatic plants.

Chemical Control to kill pond weeds

Chemical Weed Control Best Practices

Follow these tips whenever using chemicals to manage weeds and algae in your water body:

  • Partially treat your pond. At one time, treat half of the pond’s surface. However, it’s vital to treat only 1/4 of your pond once during hot weather or when addressing heavy growth and wait the full 14 days before re-applying.
  • During warmer weather or while treating high growth, this helps reduce the danger of fish loss.
  • Use a weed cutter and rake to remove as much dead material as possible once the weeds have browned and died. This keeps sludge and dead plant material from accumulating.

Emergent Weed Control

Emergent weeds, such as bulrush and water primrose, are hardy and, because of their rapid growth, can quickly become invasive.

Emergent weeds grow in only a few inches of water rather than being only aquatic or terrestrial. Some cattail species, phragmites and purple loosestrife, bulrush, and alligator weed are examples of invasive plants.

These invasive species frequently grow along lake embankments and cover the coastline in dense growth, making access difficult.

If manual measures cannot control emergent lake weeds, a systemic herbicide administered directly to the aquatic weed may be required.

Glyphosate is a cost-effective and effective herbicide for controlling aquatic weeds; however, depending on your location, the herbicide brand, and the weed you’re attempting to control, you may need to get a permit to use it.

The disadvantage is that you won’t be able to use the same substrate as other plants.

Floating Aquatic Weed Control

Many lilies can crowd a pond and block sunlight, and any plant can become a “weed” under the right conditions, reducing nutrients.

Floating weeds live in shallow water that is only a few meters deep. Water lilies, duckweed, water lettuce, water hyacinth, and other floating weeds are common nuisances.

Floating weeds are frequently easier to remove than emergent weeds because their rhizomes are less extensive and more susceptible to hand and chemical removal procedures.

Some floating weeds, such as water lilies and spatterdocks, have rhizomes, while others, like water lettuce, grow atop the water’s surface without root structures and can be raked or skimmed away.

If the weeds have become more established, contact, or systemic herbicide may be required. Some contact herbicides operate swiftly on a wide range of emergent, submerged, and floating weeds, with the benefit of not lingering in the water system for long periods before breaking down.

This means your fish and other species are less likely to be harmed, although, in the wrong conditions, there can be short-term oxygen depletion.

How To Kill Pond Weeds

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