Home / Publications / People & Ecosystems / Pilot analysis of global ecosystems: Freshwater systems

Freshwater systems: Biodiversity

One fundamental service provided by freshwater systems is habitat for a wide range of species.

  • Humans use these animals and plants for food, crops, skins, medicinal products, ornamental products (such as aquarium fish), biological control of insects and weeds, and increasingly for recreational purposes.
  • Freshwater biodiversity helps maintain ecosystem functions and ecosystem services, such as primary productivity, water purification, nutrient recycling, and waste assimilation.

Physical alteration, habitat loss and degradation, water withdrawal, overexploitation, pollution, and the introduction of non-native species all contribute directly or indirectly to declines in freshwater species.

Assessing the condition of aquatic species is of critical importance if we are going to try and preserve the integrity of these ecosystems and the goods and services we derive from them.

The following summarizes key findings of the PAGE study regarding the condition of freshwater systems, as well as the quality and availability of data.

Conditions and trends

  • Freshwater ecosystems harbor an extraordinary concentration of species; approximately 300 new freshwater species are described each year. World Wildlife Fund-US (WWF-US) has identified 53 freshwater ecoregions around the world as priority areas for conservation, based on their unique assemblage of species, habitats, and ecological or evolutionary phenomena, while the WCMC has identified 136 areas of high freshwater biodiversity around the world.
  • Physical alteration, habitat loss and degradation, water withdrawal, pollution, overexploitation, and the introduction of nonnative species all contribute to declines in freshwater species.
  • More than 20 percent of the world’s freshwater fish have become extinct or been threatened or endangered in recent decades.
  • Of the 108 large basins analyzed, 27 have high fish species richness. More than half of these basins are in the tropics, and the rest are in central North America, India, and China.
  • Evidence shows that freshwater species, such as amphibians, fish, and wetland-dependent birds, are at high risk of imperilment in many regions of the world. In the United States and parts of Canada, however, 66 percent of the populations of wetland birds are increasing.
  • The intentional or accidental introduction of nonnative species in freshwater systems is a global phenomenon. Evidence for North America, one of the best-documented regions, shows that the introduction of alien species not only has contributed to the extinction and imperilment of native fauna but also has substantial associated economic costs.
  • Modeled estimates of future species extinction rates suggest that the rates for freshwater animal species are five times higher than for terrestrial species.
  • The growing concern for species, the maintenance of pristine habitats, and the need to maintain other goods and services, such as clean water, is driving the trend, in some countries, to restore and rehabilitate freshwater systems.

Information status and needs

  • Direct measurements of the condition of biodiversity in freshwater systems are sparse worldwide. Basic information on freshwater species for many developed nations and most of the developing world is lacking, as well as threat-analyses for most freshwater species. This makes analyzing population trends impossible or limited to a handful of well-known species.

  • Information on nonnative species is frequently anecdotal and often limited to records of the presence of a particular species, without documentation of the effects on the native fauna and flora. Spatial data on invasive species are available for few species, mostly in the United States and Australia.
  • Excellent trend data are available for bird populations in the United States and Canada, and other available regional data are good but lack long-term population trends, such as data on the distribution of important bird areas from BirdLife International.
  • At a minimum, there should be monitoring of key indicator species and monitoring of the presence or introduction of nonnative species and their impacts on native fauna and flora.

Quality and availability of data

PAGE measures and indicators

Data sources and comments

Important areas and ecoregions for freshwater biodiversity

  • Olson, D. and E. Dinerstein. 1999. The Global 200: A Representation Approach to Conserving The Earth’s Distinctive Ecoregions. Draft Manuscript, March. Washington, DC: World Wildlife Fund (WWF-US).

  • Groombridge B. and M. Jenkins. 1998. Freshwater Biodiversity: a Preliminary Global Assessment. World Conservation Monitoring Centre, Cambridge, U.K.: World Conservation Press.

Both analyses are priority-setting exercises for conservation, based on existing data and expert opinion.

Fish species richness and endemism by river basin
  • Revenga, C., S. Murray, J. Abramovitz, and A. Hammond, 1998. Watersheds of the World: Ecological Value and Vulnerability. Washington, DC: World Resources Institute.

Data compiled for the World Resources Institute by the World Conservation Monitoring Centre (WCMC).

Additional information comes from:

  • Kottelat, M. and T. Whitten. 1996. Freshwater Biodiversity in Asia with Special Reference to Fish. World Bank Technical Paper No. 343. Washington, DC: The World Bank.

  • Oberdorff, T. 1997. Muséum National d’Histoire Naturelle, Lab. D’Ichtyologie Général et Appliquée, Paris, France. Unpublished data provided to WRI.

Biological distinctiveness index for North America

Abell, R.A., D.M. Olson, E. Dinerstein, P.T. Hurley, J.T. Diggs, W. Eichbaum, S. Walters, W. Wettengel, T. Allnutt, C.J. Loucks, and P. Hedao. 2000. Freshwater Ecoregions of North America: A Conservation Assessment, Washington, DC: World Wildlife Fund-United States.

Regional priority-setting analysis for conservation, based on a combination of existing environmental data and expert opinion.

Bird population trends in the United States and Canada

Data are from the North American Breeding Bird Survey, which is organized by the Patuxent Environmental Science Center. Data used in this report are limited to wetland-dependent species. Population trends cover the period 1966-98.

Global amphibian population census

Data are from the:

  • DAPTF (Declining Amphibian Populations Task Force) Website available on-line at: http://www.open.ac.uk/daptf/. Viewed 8/19/99.

DAPTF is a network of more than 3,000 scientists working in 90 countries.

Threatened species and habitats in North America, the Middle East, and Europe

Data for North America are from:

  • Abell, R.A., D.M. Olson, E. Dinerstein, P.T. Hurley, J.T. Diggs, W. Eichbaum, S. Walters, W. Wettengel, T. Allnutt, C.J. Loucks, and P. Hedao. 2000. Freshwater Ecoregions of North America: A Conservation Assessment, Washington, DC: World Wildlife Fund-United States.

These data cover threat status for North American fish and reptile species. Data for Europe and the Middle East are from BirdLife International. Data are for threatened bird species and important bird areas in these two regions.

Presence of nonnative species: introduced fish, zebra mussel in the United States, and water hyacinth distribution

Introduced fish species information is from

  • DIAS (Database on Introduction of Aquatic Species) Website. 2000. Available on-line at:http://www.fao.org/fi/statist/fisoft/dias/index.htm. Viewed 9/11/00.

Data on zebra mussel expansion are from the

  • USGS (U.S. Geological Survey). Zebra Mussel Website. Available on-line at: http://nas.er.usgs.gov/zebra.mussel/docs/sp_account.html#HDR1. Viewed 7/19/00.

Data on global distribution of water hyacinth are from a variety of sources. Water hyacinth distrubution in the United States is from the Aquatic Nuisance Species Task Force, cochaired by the USFWS and the National Oceanic and Atmospheric Administration (NOAA).