Nature, landscape and biodiversity

Exotic species in fresh water, 1900-2010

You are currently viewing an archived version of a closed indicator. The most recent version containing the reason for closing the indicator can be viewed here.

There has been a considerable increase in the number of new species found in Dutch surface waters. While most new species enter the Netherlands as a result of the trade in pond and aquarium plants and animals, the construction of the Rhine-Danube canal has also enabled many new fish and macrofauna species to reach new habitats in the Netherlands.

Considerable increase in new species

There has been a substantial increase in the number of new species establishing in the Netherlands, particularly in recent decades. The number of new species found varies with the species group. The group with the smallest number of new species is that of fish, but these do make up 40% of the total number of species in the Netherlands, against just 3% for macrofauna and 8% for aquatic plants.

Introduction of species as the main cause

The main cause of the establishment of new species is their introduction through trade in pond plants and animals, although the reason can vary for different species groups. In the case of fish, there are three important factors: the trade in pond fish, the introduction of species for angling and fisheries, and shipping. The opening of the Rhine-Danube canal in 1992 also resulted in a large increase in the number of macrofauna and fish species in Dutch waters. Species that were previously unable to reach the Netherlands were now able to travel through the canal from the Danube into the Rhine river basin. By contrast, no fish have been recorded as having colonised the Danube river basin from the Rhine river basin. More species are expected to reach the Netherlands, so that the number of new species will increase even further.
As regards new macrofauna species, one of the main causes is the introduction of various lobster species, such as the red swamp crayfish (Procambarus clarkii). These species are still traded in garden centres, but threaten the environmental and ecological quality of Dutch water bodies.

Effects on ecology

Many new species do not threaten the existing ecosystem, as they are normally only found in low numbers, but they may sometimes be found in such high concentrations locally that they do have a significant effect. Some new species of aquatic plants cause problems because they spread very quickly and can lead to water management problems. Floating pennywort (Hydrocotyle ranunculoides) can cause severe problems on a local scale. Almost all the Dutch district water boards remove floating pennywort because of the problems it can cause.
The introduced pumpkinseed sunfish (Lepomis gibbosus) has a harmful effect on pools because it eats amphibians and dragonfly larvae. There are significantly fewer amphibians and dragonfly larvae in pools with large numbers of pumpkinseed sunfish, causing a decline in biodiversity. The presence of pumpkinseed sunfish in pools is therefore considered to be detrimental. The fathead minnow, Pimephales promelas, has been found in the Netherlands since 2007. This species, also introduced, is a threat to other fish as it carries bacteria that can cause a fatal disease. The fathead minnow is actively controlled, but also continues to be sold in garden centres.


  • Kleef, H.v., G. van der Velde, R.S.E.W. Leuven en H. Esselink (2008) Pumpkinseed sunfish (Lepomis gibbosus) invasions facilitated by introductions and nature management strongly reduce macroinvertebrate abundance in isolated water bodies. Biol. Invasions 10.
  • Weijden W. van der, R. Leewis, P. Bol (2007). Biological Globalisation. Bio-invasions and their impacts on nature, the economy and public health. Utrecht, KNNV Publishing.

Archief van deze indicator

Referentie van deze webpagina

CBS, PBL, RIVM, WUR (2014). Exotic species in fresh water, 1900-2010 (indicator 1355, versie 04 , 7 June 2014 ). Centraal Bureau voor de Statistiek (CBS), Den Haag; PBL Planbureau voor de Leefomgeving, Den Haag; RIVM Rijksinstituut voor Volksgezondheid en Milieu, Bilthoven; en Wageningen University and Research, Wageningen.

Het CLO is een samenwerkingsverband van CBS, PBL, RIVM en WUR.