Invasive aquatic plants in the pond: identify and take action

Updated November 1, 2026 · By the Foudebassin experts, experts since 1998

Not all plants that take over a pond are "invasive" in the legal sense. Three families coexist: regulated exotic species (water primrose, Brazilian waterweed, water hogweed, Nuttall's waterweed, Helms's water primrose), non-listed but monitored exotic species (duckweed, duckweed, Canadian waterweed), and native species that proliferate because the water is rich (water milfoil, water pepper, water hogweed).

The solution involves three steps: identify before acting, never cut a plant that multiplies by fragments into pieces, remove it by hand, and then dispose of it away from the water. No chemical products have any place in a body of water, and the cause is then addressed: excess nutrients.

Table of Contents

1. Exotic, invasive, native: what are we talking about?
2. Recognizing the main species
3. When the overgrown plant is native
4. What the law says in Belgium and France
5. Taking action in 4 steps
6. After removal: addressing the cause
7. Frequently asked questions

Exotic, invasive, native: what are we talking about?

The word "invasive" is used incorrectly all over the place. One plant can cover half a pond without being invasive in the regulatory sense, while another, inconspicuous at first, may be banned from sale. The table below helps you identify what you have in front of you.

Recognizing the main species

To identify a plant, three clues are often enough: the shape of the leaves, the length and growth habit of the stem, and the flower, if it has one. The diagram provides an initial guide, while the following table details the key features.

Features based on the CBN de Bailleul guide to invasive exotic plants. Waterweeds and water hogweed look alike: at the slightest doubt, ask for an opinion based on a photo.

When the overgrown plant is native

A native plant that grows vigorously is not breaking the law: it is a message. The water is rich, often because the sludge releases nutrients and additional inputs are added (leaves, food, runoff). Constantly pulling it out without addressing the cause is like emptying a bathtub without turning off the tap.

The najas marina is a classic example. For duckweed, we detail two approaches in our articles on duckweed in a pond and removing it safely without harming fish. The whole is part of the balance described in our healthy natural pond guide.

Koi carp is sometimes cited as a solution. Trials show that it prefers certain plants (water milfoil, water hogweed, Canadian waterweed) and neglects water pepper, and its introduction is regulated: we return to this in our article on types of pond carp, as well as on the number of koi carp.

What the law says in Belgium and France

In practical terms: a plant on the list cannot be bought, replanted, given away, or discarded in the wild. In Wallonia, duckweed, Canadian waterweed, and duckweed are in Annex IV, while Helms's water primrose and water hogweed are in Annex III. If in doubt, report the plant to your local municipality or on the Walloon biodiversity observatory. Flanders and Brussels have their own rules: check locally.

Taking action in 4 steps

1. Identify. Photograph the leaves, stem, and flower, then compare them with the guide above. If the species is on the Union list, report it to your local municipality.
2. Block the exit. Before any pulling, place a filter downstream or around the area. The CBN de Bailleul cites 1 × 1 cm mesh for Nuttall's waterweed and a 1.5 mm net for duckweed.
3. Remove by hand. For small areas, pull it out by the roots by hand, with a fine rake or a hand rake, collecting every fragment. For water primrose, allow at least two passes in the first few years. Do not settle for just mowing: cutting alone produces fragments.
4. Dispose of it. In sealed bags, stored away from the wetland area and flood zones. Never in the water, a ditch, or a waterway.

For floating mats and small debris, a very fine mesh skimmer does most of the work. This is the equipment we keep close at hand by the water.

In addition: limit the regrowth of submerged plants

Against submerged plants (water milfoil, waterweed, water hogweed, water primrose, etc.), a pond dye can complement manual removal: it filters some of the light and limits the photosynthesis of submerged plants and algae. According to the sheet: 2 bags of 100 g per 1,000 m², 4 to 6 weeks of action depending on sunlight and water renewal, to be started in spring before full growth. According to the manufacturer, it is compatible with fish and swimming at the recommended doses. For large areas: 10-bag format.

It does not act on emergent or floating plants (water primrose out of the water, water hyacinth, etc.). For regulated species (EU Regulation 1143/2014), careful pulling, waste disposal, and reporting remain the basis; the dye complements this to limit submerged regrowth.

After removal: address the cause

A proliferating plant feeds on what the water offers it. We therefore reduce nutrients at the source: leaves collected before they sink, moderate feeding, mowing, and fertilizers kept away from the water. We also oxygenate the bottom, because rich, oxygen-deprived sludge releases nutrients.

For organic sludge, Aquipond Bactovase is the solution we use to support the breakdown of this reservoir; the sheet offers a dosage calculator according to the surface area. Our article on sludge treatment explains the method.

Finally, replant local species: they shade, absorb nutrients, and take up the space. Our list of filtering aquatic plants and that of floating plants help you choose; always check that the species is not regulated.

• The plant is identified in a photo, and its status verified.
• A filter is placed downstream before any removal.
• The plants are removed whole, without being cut on site.
• The plant waste is in sealed bags, away from the wetland area.
• Nutrients are reduced: leaves, food, sludge.
• Only local, non-regulated species are replanted.

Frequently asked questions

How to recognize an invasive aquatic plant?

Look at the shape of the leaves, the length of the stems, and the presence of flowers, then compare them with the guide in this article. If in doubt, photograph the plant and send the photos to your local municipality or a specialized organization: several neighboring species, such as waterweeds, look very similar.

Are waterweed and water milfoil invasive plants?

Nuttall's waterweed is on the European Union list, Canadian waterweed is exotic but not listed at this level, and water milfoil is a native plant. The latter can proliferate in rich water, without being regulated as invasive.

Can I buy or replant a plant on the European list?

No. For species on the European Union list, sale, possession, cultivation, and introduction into the wild are prohibited. In France, the Order of February 14, 2018, also prohibits their transport, use, exchange, and purchase.

Should I mow or cut the beds of plants?

Not alone. For water primrose, water hogweed, or Nuttall's waterweed, mowing produces fragments that regrow. We prefer manual removal, with a net downstream, and the complete disposal of the removed plants.

What to do with the pulled plants?

Put them in sealed bags and store them away from the wetland area and flood zones. Composting is only possible if no more fragments can regrow, for example after complete drying for duckweed. Never throw them in a ditch or waterway.

Is koi carp a solution against plants?

It is neither simple nor universal. It prefers certain plants to others, its introduction is subject to authorization in France, and it does not address the cause, that is, the excess of nutrients. Our article on types of carp details the conditions.

Is a dye enough against invasive plants?

No, it does not replace removal. The dye filters some of the light and limits the photosynthesis of submerged plants, but it does not act on emergent or floating plants. For regulated species, careful manual pulling, waste disposal, and reporting remain the basis; the dye complements this to limit submerged regrowth.

To go further

• Natural pond: the guide for healthy water all year round
• How to treat najas marina or najas pectinata?
• Duckweed in a pond: how to get rid of it permanently
• How to maintain and clean a natural pond?
• How to treat sludge in a natural pond?
• List of filtering aquatic plants
• Types of pond carp: how to choose

Sources consulted: EEE Resource Center: Union list · EPPO: list update, July 2025 · CBN de Bailleul: guide to invasive exotic plants · UVCW: list of invasive exotic plants, Wallonia

The Foudebassin experts, experts since 1998. Article written using the sources above and our pond experience.