Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

View Data for At-Risk Species by Risk Category View Data for At-Risk Species by Region

What Is This Indicator, and Why Is It Important? This indicator reports on the relative risk of extinction of native freshwater species. The risk categories are based on such factors as the number and condition of individuals and populations, the area occupied by the species, population trends, and known threats. Degrees of risk reported here range from very high (“critically imperiled” species often are found in five or fewer places or have experienced very steep declines) to moderate (“vulnerable” species often are found in fewer than 80 places or have recently experienced widespread declines). In all cases, a wide variety of factors contribute to the overall ratings. “Freshwater species” live in freshwater, wetland, or riparian habitats during at least part of their life cycle and depend on these habitats for survival.

Species are valued for a variety of reasons: they provide products, including food, fiber, and, more recently, genetic materials; they are key elements of ecosystems, which themselves provide valuable goods and services; and many people value them for their intrinsic worth or beauty.

Why Can't This Indicator Be Reported? This indicator reports on fish; amphibians and reptiles; aquatic mammals; butterflies; mussels; snails; crayfishes; fairy, clam, and tadpole shrimp; dragonflies and damselflies; and mayflies, stoneflies, and caddisflies. Data on freshwater and wetland plants are not included because additional analyses are required to categorize correctly the habitats of all North American plants.

See also the national at-risk species indicator and the indicators for at-risk coastal, forest, and grassland and shrubland species, as well as those for species in farmlands and urban and suburban areas.

What Do the Data Show? About 13% of native freshwater species are critically imperiled, 8% are imperiled, and 4% are or may be extinct. When vulnerable species (11%) are counted, about a third of freshwater animal species are considered “at risk.” Hawaii and the Southeast have a much larger percentage of at-risk freshwater species than any other region.

Interpreting these figures is complicated, however, because some species are naturally rare. Thus, the rankings are influenced by differences among regions and species groups in the number of naturally rare species, as well as by different types and levels of human activities that can cause species declines. Interpretation of these data will be greatly enhanced when information on population trends for these at-risk species becomes available.