'Big Muddy' Is Most Endangered River

April 11 -- In May of 1804, Meriwether Lewis and William Clark set out on an expedition across the Louisiana Territory. They traveled much of the way on a 2,500-mile, slow-moving river that was quickly dubbed the "Big Muddy."

Today, the mighty Missouri River — part of the longest river system in the United States — is in trouble. According to the environmental group American Rivers, which today released its 16th annual list of the country's most endangered rivers, the Missouri is in the worst shape, followed by the Canning River in Alaska and the Eel River in California.

The group says the main threat to the Missouri River are six dams that are pushing several river wildlife species to the brink of extinction, all for the sake of a small amount of barge traffic. American Rivers has called upon government agencies to modify the operations of these dams.

"The [Army] Corps [of Engineers] continues to run the Missouri River to benefit ahandful of barges," says Rebecca Wodder, president of American Rivers. "It is time to prevent species extinction, tap the Missouri's great economic potential for recreation and tourism and meet the modernneeds of riverside communities."

The Environmental Protection Agency did not immediately respond to calls from ABCNEWS.com seeking comment on the report.

Electricity Generation Takes Its Toll

Wodder attributes the devastating environmental damage to many of the rivers on the list to outdated ways of developing and using energy. Power plants and the quest to find more fossil fuel in areas near some of these rivers are primarily to blame for the dramatic increase of pollutants that are lethal too the rivers' wildlife populations, she says.

"Coal-fired plants … are the largest uncontrolled source of toxic mercury into the environment," Wodder says. “Mercury contaminates fish eaten by more than 7 million Americans, despite health advisories in 40 states."

Acid rain, the transfer and deposit of pollutants and fertilizer through rainfall, is also a major factor that has contributed to the endangerment of many of the nation’s rivers and surrounding ecosystems. The Paine Run River in Virginia’s Shenandoah National Park — which ranks as 11th on the list — is one victim succumbing to acid rain, Wodder says.