According to conservation outfit American Rivers, the section of the Colorado River flowing through the Grand Canyon is most endangered freshwater way in the United States.

Every year since 1984, American Rivers puts out its "America's Most Endangered Rivers" report. This year's report lists threats like harmful human development, groundwater depletion and uranium mines as just a few of the reasons why one of North America's most iconic stretches of river tops the 2015 list. It's the third year in a row the Colorado has held the dubious distinction.

"The Grand Canyon is facing the biggest threats in a generation," Bob Irvin, president of American Rivers, said in a press release. "The Colorado River in the Grand Canyon is an irreplaceable national treasure that should be preserved for all of us, for all time. The Grand Canyon is not for sale."

The new reports focuses on two key development projects, which environmentalists say will put undue pressure on the vulnerable water system. The first is a plan to construct several large commercial buildings and some 2,200 homes in Tusayan, Ariz., a small resort town near the south entrance to Grand Canyon National Park. The report's authors say pollution and groundwater depletion from the project threatens the Colorado.

The second plan, the Grand Canyon Escalade project, calls for construction of a two million square-foot tourist development that enables large numbers of visitors to visit the bottom of the canyon by way of tram lines and stairways. Critics contend the construction will pollute the river and upset the fragile ecosystem -- an ecosystem that holds the last remaining populations of some of the Southwest's rarest native aquatic species.

Developers argue their plan will open up one of the world's greatest treasures to everyday visitors without risking the river's aesthetic or ecological health.

"Is 1,500 feet (of river) too much to ask for the average visitor who doesn't have the time to take a 12-day river trip?" Lamar Whitmer, managing partner of Confluence Partners, the group behind the Escalade project, asked The Arizona Republic. "I don't think gondola trams have ruined Switzerland. They're not going to ruin Grand Canyon."

Coming in second on the new list is the Columbia River, which runs through Washington and Oregon and provides water to millions of residents in the Pacific Northwest. Conservationists argue that outdated dams along the waterway are diminishing healthy runs of salmon and other fisheries, which ultimately upset valuable food chains both in the river the Pacific Ocean.

Also listed are: Tennessee's Holston River, Montana's Smith River, South Carolina's Edisto River, and Alaska's Chuitna River. The full list and report are available on America Rivers' website.