America's most endangered river is the Potomac, which flows through the capital of the United States, says the nonprofit organization American Rivers in its 2012 annual report.

The Potomac was placed at the top of American Rivers' annual list to alert the nation to the fact that Congress is considering cuts to national clean water protections, just as rivers nationwide are facing threats from natural gas drilling, pollution and new dams.

The urgency of this alert is highlighted by the fact that it is taking place during the Clean Water Act's 40th anniversary year.

"This year's Most Endangered Rivers list underscores how important clean water is to our drinking water, health, and economy," said Bob Irvin, president of American Rivers.

Before the Clean Water Act was enacted in 1972, the Potomac was "a cesspool of sewage and industrial pollution," American Rivers points out.

Now, due to the Clean Water Act, the Potomac is cleaner and safer for drinking, boating, and fishing. But the Potomac is still suffering, says American Rivers, citing a University of Maryland report card has given the river a "D" grade for water quality for the past two years.

American Rivers and the other clean water advocacy groups are calling on Congress to kill any legislation that weakens the Clean Water Act or prevents the Environmental Protection Agency and the U.S. Army Corps of Engineers from restoring protections for small streams and wetlands under the Act.

American Rivers also called on the Obama Administration to finalize guidance clarifying the scope of the Clean Water Act and issue a rule "to ensure that all waters get the protections Americans expect and deserve."

Today American Rivers announced the kickoff of its National River Cleanup. For more than 20 years this program has mobilized hundreds of thousands of volunteers to pick up trash from plastic bags to old tires to large appliances from rivers and streams.

Now in its 27th year, the annual America's Most Endangered Rivers report is a list of rivers at a crossroads. Over the years, the report has helped spur many successes including the removal of outdated dams, the protection of rivers with Wild and Scenic designations, and the prevention of harmful development and pollution.