Pike fishing for fish balance and clear water in VisKringloop

The VisKringloop in Wieringermeer was created in 2020 as a clear, plant-rich, and water-rich area with many shore zones. In recent years, carp populations have expanded significantly, posing risks to water quality and ecological balance. To restore that balance, the Hollands Noorderkwartier Water Board released young pike into the VisKringloop in January 2026. Fishing is strictly prohibited in this habitat and breeding ground for migratory fish species.

Fish stock over 95% carp

During monitoring in 2021, a total fish stock of 67.4 kg per hectare was recorded. Of this, 64.5 kg per hectare consisted of carp — more than 95% of the total fish stock. This dominance can lead to cloudy water and a decline in aquatic plants. As a result, other fish species that depend on aquatic plants do not have a chance to establish themselves.

Why intervene?

Although pike live in the surrounding waters and fish passages are present, various studies show that pike have not yet established themselves in the area after five years. As a result, there is a lack of natural predators that normally ensure balance in the fish population. In healthy polder waters, pike make up about 10–20% of the fish biomass. This natural predation keeps carp and other fish species in balance, keeping the water clear and allowing plant growth to develop better. Without this predation pressure, this potentially diverse plant-rich ecosystem could turn into a murky, monotonous water system, which is not desirable.

With the presence of pike, HHNK expects the VisKringloop to continue to develop into a stable, clear, and species-rich water system—exactly as intended when it was constructed. A WFD fish stock survey is conducted periodically in the area. From this, we can also determine the extent to which the pike have definitively taken their place in the VisKringloop.