Colorado River named most endangered in US

(Courtesy Flickr user Al_HikesAZ/Creative Commons) 

That stretch topped the America's Most Endangered Rivers report in 2013 as well. The list of threatened waterways is published every year by the environmental advocacy group American Rivers.

The report cited a tourism construction project, radioactive pollution and a proposed expansion of groundwater pumping outside of Grand Canyon National Park as the river's top threats. 

"Unless the Department of the Interior acts to stop these threats, one of our nation’s greatest natural treasures will be scarred forever," the report says.

The proposed  Grand Canyon Escalade project includes a tram that would bring 10,000 people into the canyon's basin per day, American Rivers says. The company behind the project called American Rivers' concerns "speculation."

“Any report must be primarily based on speculation rather than any actual facts as plans for construction have not been finalized or released,” a public information officer at Confluence Partners, LLC., the company managing the project, told Al Jazeera.