The Potomac River is much healthier today than it was 40 years ago, when its chemical-laced, sewage-laden waters helped inspire the 1972 Clean Water Act. But the iconic Washington, D.C., waterway still has a long way to go, as suggested by its No. 1 ranking in a new list of America's 10 "most endangered rivers."

The list, released annually by conservation group American Rivers, doesn't necessarily name the country's 10 most polluted rivers. As American Rivers explains on its website, it selects the most at-risk rivers each year based on three criteria:

  • a major decision in the coming year that the public can help influence;
  • the significance of the river to human and natural communities;
  • the magnitude of threats to the river and associated communities.
The significance of the Potomac is hard to miss: It's nicknamed "the nation's river" because it flows through the U.S. capital, and it supplies drinking water to 5 million people in four states plus the District of Columbia. It has been on American Rivers' list before, but made the top spot in 2012 as a way of highlighting efforts in Congress that could weaken the Clean Water Act. Because that law helped save the Potomac from rampant pollution last century — and because the Potomac has national symbolic value — American Rivers says it's "emblematic of what's at stake for rivers nationwide," calling it a natural choice for this year's No. 1.

"When members of Congress fill a glass of water or drink their morning coffee, that water comes from the Potomac River," American Rivers president Bob Irvin says in a news release. "It's time to draw clear connections between healthy rivers, drinking water and public health in Washington, D.C., and in communities nationwide."

American Rivers isn't the only one pointing out the Potomac's problems. In its annual report card on the Chesapeake Bay ecosystem, the University of Maryland has given the river a "D" the past two years, up from a "C" in 2009. The 2011 report cited "declines in water clarity and benthic community" for the low grade. While the Potomac was threatened in the past by raw sewage and industrial dumping, it faces subtler threats today, such as toxic runoff from farms, cities and mines.

"Thanks to the Clean Water Act, you no longer see and smell most of the problems in the watershed, and no president is currently calling the Potomac a 'national disgrace,'" Ed Merrifield, president of Potomac Riverkeeper, said in a statement. "But the hidden problems are many and in some ways worse than when the problems were palpable. ... The urban, suburban and agricultural stormwater runoff causes serious problems throughout the watershed, at times impairing the use of the river. The past fish kills and pervasive intersex fish issues due to the 'chemical soup' the fish swim in have made national headlines for years."

For the other nine rivers on the list, threats include new dams and reservoirs, dredging plans, coal mining and natural gas development. In a press release issued Tuesday, American Rivers calls on the Obama administration "to finalize guidance clarifying the scope of the Clean Water Act and ... to ensure that all waters get the protections Americans expect and deserve."

The full list of troubled waterways is below, including the states where they flow and the threats cited by American Rivers. See the official list for more information about each river, such as what's at stake and how to help.

  1. Potomac River (MD, VA, PA, WV, DC) — pollution
  2. Green River (WY, UT, CO) — water withdrawals
  3. Chattahoochee River (GA) — new dams and reservoirs
  4. Missouri River (IA, KS, MO, MT, NE, ND, SD, WY) — outdated flood management
  5. Hoback River (WY) — natural gas development
  6. Grand River (OH) — natural gas development
  7. South Fork Skykomish River (WA) — new dam
  8. Crystal River (CO) — dams and water diversions
  9. Coal River (WV) — mountaintop removal coal mining
  10. Kansas River (KS) — sand and gravel dredging

And to learn more about why the Potomac River is imporant to people and wildlife in its watershed, check out this video released last year by the Nature Conservancy:

Also on MNN:

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Potomac tops list of 'endangered rivers'
The Washington, D.C., river epitomizes the ecological dangers that plague many U.S waterways, according to a national environmental group.