The Delfland Water Board has started trapping American crayfish at ten locations. This invasive alien species poses a growing threat to aquatic ecosystems and water quality. The approach will be significantly expanded in the coming years: by 2027, it will involve 170 trapping locations along a total of 59 kilometers of riverbank.
By 2027 at the latest, water quality and ecology must meet the requirements of the European Water Framework Directive (WFD). Delfland works every day on clean and healthy water. To achieve the WFD goals, the water board invests specifically in wet ecological zones (NEZs), such as nature-friendly banks, fish spawning grounds, and aquatic plant zones. Crayfish also cause significant damage in these areas.
Harmful invasive species
According to ecologist Wilco de Bruijne, intervention is necessary: ’The crayfish first appeared in our area in the 1980s. Conditions here are favorable and they reproduce rapidly. By now, we are talking about tens of millions of animals. If we do nothing, the impact on aquatic nature and water quality will be incalculable.’
American crayfish cause damage in various ways. They dig deep burrows, which can cause banks to subside and damage dikes. This increases the risk of flooding. Additionally, they eat aquatic plants and churn up the bottom, leading to turbid water. As a result, biodiversity declines and water quality deteriorates.
Targeted approach in vulnerable areas
The catch initially focuses on locations where NEZs have recently been constructed and on watercourses with young submerged aquatic plants. Project leader Ad Valkenburg: ‘This is a large-scale operation for us. Ultimately, we will deploy thousands of catch containers that need to be emptied weekly. That is why we are working in phases and learning as we go. In doing so, we are also measuring the effects on water quality.’
First results show the extent of the problem
To empty the traps, Delfland employs two professional fishermen via a contractor. The traps are designed to be as animal-friendly as possible, with minimal risk of bycatch. The caught lobsters go to Craw Fish Farm, a Dutch company focused on sustainable food production.
The first catches show that the lobster population is large in many locations. The number of catches is expected to increase further as it gets warmer and the lobsters become more active.
A hefty price tag
The approach requires a substantial investment. The Delfland board has made 7 million euros available for 2026 and 2027. The goal is to reduce the crayfish population per location by approximately 80 percent, so that aquatic nature can recover.
The total costs for the protection of all wet ecological zones are estimated at 13 million euros in the first year and 7.3 million euros per year thereafter. This concerns only the control of crayfish. Restoration of banks and dikes is in addition to this.
Delfland wants a national approach
Although Delfland is now taking measures itself, the responsibility for combating American crayfish lies with the central government. Water Board Member Stijn van Boxmeer: ’We are now taking responsibility for the artificial aquatic nature in our area, but according to the Invasive Alien Species Ordinance, the control of this invasive alien species lies with the Ministry of Agriculture, Fisheries, Food Security and Nature (LVVN). Furthermore, Delfland is not the only one suffering from American crayfish. They occur throughout the low-lying Netherlands, in all peat meadow areas. The scale of the problem therefore also calls for a national approach.’
Text & Images: Delfland Water Board
Translation to English: The Hague Online
The Netherlands and water are inextricably linked. However, strong dikes, clean ditches, and pure water are essential requirements for a safe environment. At the Delfland Water Board, we take care of the water. So that you, together with all the residents of our area, can enjoy living, working, and relaxing in this beautiful, water-rich environment.