Control of Invasive Exotic Aquatic Plants in Weerribben-Wieden (LIFE-IAAS)

 Invasive alien species are plants and animals that do not naturally occur in the Netherlands but have arrived here due to human actions. They may have been introduced through horticultural sales, aquarium releases, or unintentionally transported via vehicles, aircraft, or boats. While not all exotic species cause problems in their new environments, some thrive to the extent that they outcompete native species. These invasive exotic species can cause significant harm to the indigenous plants and animals within the ecosystems they invade.

Cabomba caroliniana and Myriophyllum heterophyllum are examples of invasive aquatic plants that have recently appeared in the Weerribben-Wieden. Originally from America, these plants are often sold in the Netherlands as popular aquarium species. When aquarium contents are dumped into local waterways, these species find themselves in a completely different ecosystem, approximately 7,500 km from their natural habitat, with no natural predators.

The invasive aquatic plants, Cabomba caroliniana and Myriophyllum heterophyllum, are rapidly spreading throughout the Weerribben-Wieden. This leads to thick overgrowth in the water, making it difficult for native plants and animals to survive. This also threatens the existence of vulnerable species in the protected Natura 2000 area.
The impact of these invasive species extends beyond the natural environment. We are observing that increasingly larger areas of water are becoming completely overgrown, which affects recreational activities such as boating, fishing, and swimming which leads to economic damage to the region. It becomes difficult to boat in the region, as the invasive aquatic plant becomes entangled in propellers. Many fish species disappear when there is insufficient swimming space available. Additionally, swimming becomes unpleasant for people. Furthermore, an increase in Cabomba caroliniana can result in the rise of freshwater snails, which carry larvae. When these come into contact with a swimmer's skin, they can cause irritation, commonly known as swimmer's itch. Moreover, the blockage of waterways can create issues with water supply and drainage, particularly during heavy rainfall.

The Province of Overijssel and it’s partners are working to protect and preserve the unique natural values in the Weerribben-Wieden. To remove Cabomba caroliniana and Myriophyllum heterophyllum from this area, approximately 7 million euros will be needed for the next five years. The European LIFE subsidy will contribute about 4.3 million euros, which accounts for 60% of the total project costs.
How we  propose to manage the invasive aquatic plants in the area:

1. Cabomba caroliniana and Myriophyllum heterophyllum will be removed from the area both mechanically and manually. This approach aims to combat the population of exotic aquatic plants and ensure that the protected native aquatic plants do not continue to decline. The goal is to reduce the coverage of invasive alien aquatic species (IAAS) to a maximum of 2%. After achieving this target, regular maintenance will involve only manual removal from the remaining small growth areas
2. The mechanical removal of invasive exotic aquatic plants is a significant undertaking. Therefore, we are also conducting pilot projects in peat pits to investigate whether we can manage the invasive exotic plants through alternative methods while effectively protecting the native ecosystem.
3. We shall raise awareness among the residents and the tourism sector about this problem and encourage contributions to its solution. We will inform residents and tourists about measures they can take to prevent the spread of these exotic species.