Invasive exotics

Exotics are plants or animals that do not occur naturally in our country, but have ended up in nature here in the Netherlands as a result of human activity. In the absence of natural enemies, they can displace native species and become a pest. We then speak of invasive exotic species.

Problems caused by exotics

There are several species of invasive exotic species in our management area that cause problems for the tasks and goals of the Water Board.

Watercourses can become clogged by explosive growth of non-native aquatic plants, which can cause problems with water supply and drainage (example: Large water pennywort, Water primrose).
Dikes and embankments can be affected by overgrowth of non-native plants (example: Japanese knotweed, Giant hogweed).
Non-native aquatic plants and animals can also harm water quality by displacing or affecting native species (example: Water crassula, American crayfish).

What does HHNK do?

We have specially trained employees who remove invasive exotic plants. Removal must be done very carefully because any remnant left behind can grow again. By intervening in time, we reduce the chance of spreading and high control costs. Known locations are checked regularly.

We are working to create a healthy water system where native species can thrive. As a result, invasive species have less chance of becoming dominant.

Our own staff keep a record of locations where invasive exotic species have been found in watercourses or on our flood defenses. We also use information on the presence of invasive exotic species from the National Database on Flora and Fauna (NDFF).

We address other owners and residents of watercourses about their responsibility to prevent problems. Where possible, we cooperate with other landowners in controlling or controlling exotics.

Water boards in the Netherlands are required by law to protect dikes and banks from burrowing damage by muskrats and beaverrats. HHNK has outsourced the control of these animals to Muskrat Management West and Central Netherlands. See the page Reporting muskrat.

Preferred species strategy

For the exotics that occur in our management area, we have determined a preferred strategy. A number of species of land plants and aquatic and riparian plants are actively controlled. These include species that cause a major nuisance (for example: Japanese knotweed, Large Water Nymph, Pearl featherweed) or species that are only present in our area to a limited extent and therefore can be completely reduced (for example: Small water primrose, Water hyacinth, Water fan). In addition, there are species that are quite common and for which efforts are made to manage the extent (example: Large duckweed fern/Azolla or Narrow waterweed). Non-native aquatic species, such as non-native crayfish, the Chinese woolly crab or exotic gobies, are not actively controlled at this time. No good control method is available to address these species.

What can you do?

Report

Do you see invasive exotics in or along water? Then submit a report via Waarneming.nl. It is also possible to use the NDFF Input App (ObsMapp / iObs or ObsIdentify) or Exoten app (ndff.nl). Please include a clear photo with the report so that it is easy to see which species is involved. This will help Map the spread of invasive exotic species. Your report will be included in the national database of the NDFF.

Prevention

Do not release plants or animals from your garden, pond or aquarium into the wild yourself. Throw your excess (water) plants in the green container and choose native species when purchasing plants.