Half the rivers in US in 'poor condition for aquatic life,' EPA survey says

A mailbox is seen at the edge of the Yazoo River near Yazoo City May 22, 2011 in Yazoo County, Mississippi.

More than half of America's rivers and streams contain water that is in "poor condition for aquatic life," with increasing pollution and erosion endangering several species, according to a survey.

The Environmental Protection Agency assessed data from 2,000 rivers and streams in 2008-2009, the most recent figures available, which showed 55 percent of waterways to be in poor biological health and unable to support healthy populations of aquatic insects and other creatures.

Twenty-three percent were in "fair shape," while 21 percent were in good biological health, the Associated Press added, citing the report. 

Reuters quoted Nancy Stone, acting administrator of the EPA's Office of Water, as saying, "This new science shows that America's streams and rivers are under significant pressure."

Rivers in the country's east were in the worst condition: More than 70 percent of streams and rivers from the Texas coast to the New Jersey coast were in poor shape.

The healthiest streams and rivers were in Western mountain areas, where only 26 percent were classified as in poor condition.

According to Reuters, the report blamed high levels of phosphorus and nitrogen, mainly caused by runoff from urban areas.

Such "nutrient pollution" increases algae levels and decreases oxygen levels which are required by fish and other aquatic life.

Other water bodies showed increases in bacteria and mercury, which are deemed a health risk.