Most U.S. river and stream miles in poor biological condition
The majority of river and stream miles nationwide are in poor condition for aquatic life, according to an unprecedented survey from the Environmental Protection Agency.
The survey is the first statistically based survey of the condition of the nation's rivers and streams, the EPA says. In 2008 and 2009, field crews sampled nearly 2,000 randomly selected river and stream sites that ranged from major rivers to small creeks.
To rate rivers and streams for their ability to sustain aquatic life, the EPA used a common index that measures the condition of insects, crayfish and other macroinvertebrates that live on the bottom of bodies of water. The survey found 21 percent of the nation's river and stream miles in good biological condition, 23 percent in fair condition and 55 percent in poor condition.
The EPA's draft report (.pdf) on its findings, released March 26, also notes chemical stressors and physical habitat stressors, but biological condition is the best indicator of the health of a body of water, the report says. "When the biology of a stream is healthy, the chemical and physical components of the stream are also typically in good condition."
The ecoregion classified as the West--California, Oregon, Washington, Idaho, Nevada, Utah, Arizona, and parts of several other states--was in the best condition, with 42 percent of river and stream miles in good condition. The rest of the continental United States fell into two ecoregions that each rated at less than 20 percent of river and stream miles in good condition.
The survey also analyzed fish tissue samples for mercury levels; most human exposure to mercury comes from eating fish. The results indicated that about 13,000 river miles have mercury concentrations that exceed the level that is safe for human health. This part of the survey only included large rivers because fish caught for human consumption are more likely to come from large rivers, where their populations are sizable.
- download the draft report, "National Rivers and Streams Assessment 2008-2009: A Collaborative Survey" (.pdf)