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
• 51 percent of U.S. crayfishes are imperiled or vulnerable.
• 40 percent of amphibians are imperiled or vulnerable.
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.
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
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.
These 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.
Freshwater Fact Sheet
Freshwater Biodiversity and Declines
• The United States is a global center of aquatic biodiversity. For several
groups of organisms, such as freshwater mussels, crayfish, snails, and
aquatic insects, the U.S. ranks first in species diversity among all
countries. The U.S. harbors two-thirds of the world’s crayfishes, 40% of
stoneflies, a third of the world’s mussels and mayflies, and one-tenth of
the world’s freshwater fishes. Source: 1
• The southeastern U.S. is one of the richest aquatic regions on the planet.
Seventy percent of the 113 imperiled species found in the
Tennessee-Cumberland Rivers and the Mobile River basin are found nowhere
else in the world. Source: 1
• Freshwater animals are the most threatened species on the planet. Seventy
percent of mussels are imperiled, along with 50% of crayfishes, and 40% of
amphibians and fishes. Forty-five percent of all listed threatened and
endangered species live in freshwater. Certain states are experiencing
extreme threats to aquatic diversity; every fish species in New Mexico has
been listed under the Endangered Species Act or proposed for such listing,
for example. Sources: 1, 2, 3, 4
• The rate of extinction of North American fishes has doubled over the
course of this century. Source: 5
• Fish harvests in the Illinois River declined by nearly 100% during this
century, while populations of migratory salmon in the Columbia River have
declined by more than 95%. Harvest in the Missouri River has decreased by
85% since 1945, and that in the Delaware River has decreased by a similar
amount. Sources: 5, 6, 7
• Populations of the 10 most common ducks in North America have declined by
more than 30 percent since the 1950’s. Source: 8
• Riparian habitats account for about seven percent of the landscape
nationwide. The US Fish & Wildlife Service estimated that 70 percent of this
habitat has been lost or altered. Other estimates reach 90 percent. Source:
Threats to Freshwater Biodiversity
• The three leading threats to aquatic animals are: alterations in natural
river flow patterns due to dams, diversions, and ground water pumping;
polluted runoff from farms and urbanizing areas; and the introduction of
non-native species that compete with natives. Source: 9
• Only two percent of rivers in the U.S. remain free-flowing and relatively
undeveloped. Source: 10
• The world’s rivers are now obstructed by more than 40,000 large dams, and
more than 800,000 small dams. The U.S. is the second-most dammed country
with some 5,500 large dams, surpassed only by China with 19,000. Source: 11
• Nearly 40 percent of U.S. waters assessed in 1992-93 remain too polluted
for fishing, swimming, and other uses. Source: 12
• Forty percent of the sediment in streams is not natural but washed from
cultivated fields. Nearly 200 million pounds of toxic and hazardous
pollutants are discharged directly to U.S. waters annually. Sources: 3, 13
• The total cost of on-site and off-site damages (such as health costs,
dredging waterways, and water treatment, but not including damage to aquatic
life) from U.S. agricultural erosion is about $44 billion/year. Source: 14
• In North America, 140 species of freshwater fish, including 40 not native
to the continent, have become established following introductions outside
their natural ranges. Source: 15
• Introduced species were a contributing factor in 68% of North American
fish extinctions over the past century. Source: 16
• As of 1985, up to 60% of the 550 billion gallons of water available per
day on average was diverted for out-of-stream uses. Global water demands are
expected to double within the next 30 years. Freshwater use is growing at
2.5 times the population growth. Supplies are presently precarious for more
than 132 million people in 20 countries; that number is expected to swell to
at least 650 million by 2025. Sources: 17, 18
• Irrigation is responsible for 81% of the total consumptive use of
freshwater withdrawn from surface and ground water in the 48 states. In the
20 leading irrigation states, this figure is about 91%; in the 17 western
states, this figure is about 87%. From the Colorado River system, 64% of the
runoff is consumed by irrigation, and an additional 32% is lost by
evaporation from reservoirs. Sources: 19, 20
• Gallons of water used to create a computer chip: 2,800 Source: 21
• Gallons of water used to make a quarter-pound hamburger: 703 Source: 21
• Gallons of soda consumed each day worldwide: 70,000,000 Source: 21
Sources of information cited in this fact sheet:
1. Master, L.L., S.R. Flack, and B.A. Stein (editors). 1998. Rivers of Life:
Critical Watersheds for Protecting Freshwater Biodiversity. The Nature
Conservancy, Arlington, VA.
2. Stein, B.A., and S.R. Flack. 1997. 1997 Species Report Card: The State of
U.S. Plants and Animals. The Nature Conservancy, Arlington, VA.
3. Palmer, T. 1994. Lifelines: The Case for River Conservation. Island
Press, Washington DC.
4. American Rivers, cited in Arizona Water Resource, April-May 1995, Vol. 4,
5. Wilcove, D., M. Bean, and P. Lee. 1992. Fisheries management and
biological diversity: problems and opportunities. In: Transactions of the
57th North American Wildlife and Natural Resources Conference. Wildlife
Management Institute, Washington, DC.
6. Ebel et al. 1989.
7. Hesse, L.W., G.R. Chaffin, and J. Brabander. 1989. Missouri River
mitigation: a system approach. Fisheries 14: 11-15.
8. US Dept. of the Interior and Environment Canada. 1986. North American
Waterfowl Management Plan: A Strategy for Cooperation. U.S. Fish and
Wildlife Service, Twin Cities, MN and Canadian Wildlife Service, Ottawa,
9. Richter, B.D., D.P. Braun, M.A. Mendelson, and L.L. Master. 1997. Threats
to imperiled freshwater fauna. Conservation Biology 11: 1081-1093.
10. Benke, A.C. 1990. A perspective on America’s vanishing streams. Journal
of the North American Benthological Society 9:77-88.
11. McCully, P. 1996. Silenced Rivers: The Ecology and Politics of Large
Dams. Zed Books, London, England.
12. U.S. Environmental Protection Agency. 1994. The Quality of Our Nation’s
Water: 1992. EPA 841-S-94-002. EPA Office of Water, Washington, DC.
13. Adler, R.W., J.C. Landman, and D. Cameron. 1993. The Clean Water Act 20
Years Later. Island Press, Washington, DC.
14. Abramovitz, J.N. 1997. Valuing nature’s services. In: Brown et al.
(Eds), State of the World. Worldwatch Institute..
15. Abramovitz, J.N. 1995. Freshwater failures: the crises on five
continents. World Watch, Sept/Oct 1995.
16. Miller, R.R., J.D. Williams, and J.E. Williams. 1989. Extinctions of
North American fishes during the past century. Fisheries 14:22-38.
17. Solley, W.B., C.F. Merk, and R.R. Pierce. 1988. Estimated Use of Water
in the United States in 1985. Circular 1004. US Geological Survey, US
Government Printing Office, Washington, DC.
18. Common Ground Vol 8 No 3, March-April 1997.
19. US Geological Survey. Estimated Use of Water in the United States in
1990. US Geological Survey, US Government Printing Office, Washington, DC.
20. Dynesius, M. and C. Nilsson. 1994. Fragmentation and flow regulation of
river systems in the northern half of the world. Science 266:753-762.
21. International Rivers Network, World Rivers Review Newsletter, Berkeley,
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