Freshwater Biodiversity

Hidden beneath the shimmering surface of our nation’s rivers and lakes is an extraordinary variety of aquatic creatures, largely unseen and unfamiliar to most of us. Rivers and lakes are the circulatory system of our nation. These ecosystems furnish a variety of services, from drinking water and recreational opportunities to transportation and food. The very quality of our lives, and freshwater species’ survival, is tied to their health.

Inhabitants of freshwater ecosystem have, as a whole, suffered far more than plants and animals dependent on upland habitats such as forests and prairies. Many of our freshwater species groups are in dire straits. The 1997 Species Report Card, released by The Nature Conservancy in cooperation with the state Natural Heritage Network, found that:

• 67 percent of U.S. freshwater mussels are vulnerable to extinction or are already extinct; more than 1 in 10 mussels may have become extinct during this century alone.

• 303 fish species - 37 percent of the U.S. freshwater fish fauna -- are at risk of extinction; 127 species have already gone extinct, mostly in this century.

• 51 percent of U.S. crayfishes are imperiled or vulnerable.

• 40 percent of amphibians are imperiled or vulnerable.
  

37% of the US freshwater fish fauna are at risk of extinction.  © The Nature Conservancy

Startling as these finding are, they are consistent with other recent assessments of the deteriorating condition of freshwater species and ecosystems in the United States. Although extinction is a natural process, scientists report that current extinction rates are on the order of 1,000 times normal rates.

Protecting and restoring watersheds will take creativity, commitment, and the involvement of local communities. The returns from such efforts will benefit not only the rich diversity of fishes and other aquatic life, but the human communities themselves.

Learn more about the threats to freshwater biodiversity. 

The United States, with 801 species, ranks seventh among countries in the world in recorded fish species. © The Nature Conservancy

The United States - A Global Center of Freshwater Biodiversity
 
Though we are a nation devoted to the beauty and recreational values of our streams, creeks, and rivers, few of us know that U.S. streamlife is exceptional on a global level, even compared with the tropics. This remarkable freshwater diversity should be a source of great national pride. Instead, it is a source of grave concern.

The United States harbors an impressive diversity of freshwater species in comparison with most other countries. For several groups of organisms the United States ranks first in the number of known species.

Although most of the world’s freshwater fish species are tropical, the United States, with 801 species, ranks seventh among countries in the world in recorded fish species. In contrast, only 193 freshwater fish species are known from all the countries of Europe and 188 species from the continent of Australia.

Freshwater invertebrates are in general less well studies than fishes, although groups such as mollusks, crayfishes, and some aquatic insects are sufficiently well known to allow for meaningful global comparisons. The United States is home to three-fifths of the world’s known crayfishes, 96 percent of which occur no place else.

Almost one-third (approximately 300 species) of all known freshwater mussels occur in the United States. The United States is also comparatively rich in freshwater snails and in an unusual assemblage of freshwater invertebrates called stygobites, which are restricted to life underground.

Although freshwater insects are less well known worldwide, again the United States ranks first among countries in described species for three relatively well-studies groups: stoneflies, mayflies, and caddisflies.
 
 
A Regional Perspective - Species at Risk 

Dramatic declines in freshwater animal species are due primarily to the intensive human use - and abuse - of their habitats. Rivers are affected by, and reflect, the condition of the lands through which they travel. Since the Clean Water Act became law in 1972, the United States has made great strides in improving water quality by controlling “end of pipe” pollution, but nonpoint source pollution - polluted and sediment-laden runoff from urban and rural areas - is still a major problem.