The stretch of the Colorado River that winds through the Grand Canyon tops a new list of the nation’s most endangered rivers, a reflection of controversial plans to reopen a uranium mine in the area and build a tramway that would take visitors to a new restaurant and river walkways on the canyon floor.

The Colorado was among ten rivers that the environmental group American Rivers identified as facing imminent threats, in a list released on Tuesday. The rivers on the list aren’t necessarily the most imperiled or polluted, says Sinjin Eberle, the group’s associate director of communications for the Colorado River Basin. Rather, they are the ones that the advocacy group is urging the public to ask government agencies to protect in the coming months.

America's most endangered rivers of 2015 Click on the dots or arrows to move through the top 10 list. 1. Grand Canyon watershed Arizona, Utah Threat Harmful development, groundwater depletion, uranium mines 2. Columbia River Washington, Oregon Threat Outdated dam operations 3. Holston River Tennessee Threat Toxic chemical pollution 4. Smith River Montana Threat Water quality, wild trout fishery 5. Edisto River South Carolina Threat Excessive water withdrawals 6. Chuitna River Alaska Threat Coal mine 7. Rogue-Smith watersheds Oregon, California Threat Nickel mines 8. St. Louis River Minnesota Threat Copper-nickel sulfide mine 9. Harpeth River Tennessee Threat Sewage pollution 10. Pearl River Louisiana, Mississippi Threat New dam NG MAPS; ANDREW UMENTUMSOURCE: AMERICAN RIVERS; GRAND CANYON TRUST; GRAND CANYON ESCALADE; ARMY CORPS OF ENGINEERS; SAVE OUR SMITH; FRIENDS OF THE EDISTO; CHUITNA COAL PROJECT; KALMIOPSIS RIVERS; Mining truth; SOUTHERN ENVIRONMENTAL LAW CENTER; TIMES-PICAYUNE; USGS

Other rivers on the list include the Columbia River in Washington and Oregon, where the group says that outdated dams have decimated populations of salmon and steelhead; the Holston River in Tennessee, which is under threat from chemical pollution; the Smith River in Montana, where the group says a proposed copper mine threatens the river’s wild trout population; and the St. Louis River in Minnesota, where the group says a proposed copper-nickel sulfide mine threatens drinking water and wildlife.

During the past several million years, the Colorado has sliced through layers of limestone, sandstone, and shale, creating a canyon in Arizona that is more than a mile deep in places. And although it’s still awe-inspiring and occasionally unpredictable, the river has been transformed by dams upstream that have altered its flows and water temperatures, as well as by pollution and nearby development. (Read more about saving the Colorado in “The American Nile.”)

Reviving a “Zombie Mine”

The 277-mile stretch of the lower Colorado is ranked first on the group’s list because of three proposals: the planned reopening of a nearby uranium mine, the proposed 1.6-mile tramway that would help tourists get from new commercial developments on the canyon’s rim to the canyon’s floor, and a major expansion of the Arizona town of Tusayan.

A mining company, Energy Fuels Resources, is seeking to reopen the Canyon Mine near the south rim of the Grand Canyon and sink an additional 1,200 feet of shaft to reach ore.

In 2012 the Obama administration announced a federal moratorium on new mining claims in the area, but four existing mines remain near the canyon.

In this short from filmmaker Pete McBride, the river becomes the narrator of a visual poem that tells the story of its history, significance, and potential future outcome.

“They’re casually called ‘zombie mines,’ because when the price of uranium goes down, the mines pause their operations and start operating again when the price rises,” Eberle says. “That’s happening right now.”

Uranium has contaminated groundwater in the area. Because of radioactive runoff on the South Rim, the National Park Service warns hikers not to drink the water in a nearby creek.

But Energy Fuels Resources spokesperson Curtis Moore said that naturally occurring uranium deposits eroding into the canyon have more impact on the park than do the mines outside its boundaries.

View Images A young man dives into the Little Colorado River in the Grand Canyon. Photograph by Pete McBride, Nat Geo Image Collection

“Unfortunately, there is a lot of misinformation about our activities,” Moore wrote in an emailed statement. “All we are doing at these small mines is removing uranium-bearing rock from a less than 20-acre site. Our mines, which are regulated as ‘zero discharge’ facilities, pose no threat to the Grand Canyon, water, or the natural environment.”

American Rivers also cites potential impacts of the proposed Grand Canyon Escalade. (See “Grand Canyon on the Precipice” to learn more.)

Since 2012, a private developer has been negotiating with the Navajo Nation to build hotels, restaurants, a dude ranch, and a spa at the rim and the gondola tramway into the canyon. Down at river level, at the confluence of the Colorado and the Little Colorado Rivers, plans include a two-story restaurant and elevated walkways. The project has not been approved by the Navajo Nation Tribal Council, and it has caused debates on the reservation and among other local tribes over whether the development would amount to a slap at Native American culture, or a much-needed economic boost. The Tribal Council might vote on the proposal this summer.

The American Rivers group is concerned about the construction of the tramway and the related attractions—how bulldozers and cranes would be lowered into the canyon, for example—and about the potential impact of new visitors arriving in the canyon via the tramway. The group also worries about water use and sewage treatment for the development at the rim.

Calls to the developer seeking comment were not returned. But on its website, Confluence Partners, a group representing developer R. Lamar Whitmer and some Navajo leaders, says that the project would not affect sacred sites and that it would be “one of the most environmentally friendly and green projects ever built."

The nearby town of Tusayan plans to expand from about 200 to more than 2,000 homes, with an additional three million square feet of commercial space, in anticipation of a tourism boom.

A Threat to Canyon’s “Spirit”

View Images At the point where the Colorado River flows past Page, Arizona, limestone formations create an area known as Gooseneck. Photograph by Pete McBride

Grand Canyon National Park Superintendent Dave Uberuaga says he is pleased that American Rivers has recognized the need to protect the park from development and mining.

“The National Park Service preserves and protects America’s special places—but even with the bodies of law that protect a place like Grand Canyon, external threats continue to be real,” he says.

But on each of these issues, Eberle says, the Interior Department, which oversees the National Park Service and the Bureau of Indian Affairs, should ensure a more sustainable future for the river, wildlife, and local communities.

“These three things all have actions that are happening in the next 12 months, and all are potentially damaging to the spirit of the canyon, the spirit of the park, and the actual health of the river itself,” Eberle says.

The Interior Department handles uranium mining permits, and with respect to the Escalade development, Eberle says, it should engage with the Navajo Nation and other tribes to seek more sustainable development.

Despite the changes over the past century, many of the river’s native species of fish and wildlife have remained resilient.

“One of the things that gets lost when we talk about the river,” says Brian Healy, the park’s fisheries program manager, is that “the Grand Canyon is a stronghold for native fish.”

The stretch of the Colorado through the canyon hosts one of the largest populations of endangered humpback chub and a spawning population of rare razorback suckers—a species that evolved more than three million years ago. Until recently, experts thought the sucker had disappeared from the area.

View Images A warm-water stretch of the lower Colorado hosts one of the largest populations of endangered humpback chub. Photograph by Pete McBride, Nat Geo Image Collection

A Symbol of the Southwest

Aside from hosting thousands of rafters and recreationists each year and supporting wildlife and fisheries, the Colorado River also is a powerful symbol of the Southwest.

Having grown up in Arizona, Roger Clark, 63, started visiting the canyon as a child and later worked as a river guide.

“It’s hard to separate who I am from the Grand Canyon,” says Clark, a program director for the conservation group Grand Canyon Trust. “It’s been a lifelong love affair.”

In the 1960s, environmental groups fought the federal government’s plans to build hydroelectric dams in the canyon. Today’s problems, Clark says, are more numerous and more complicated. Groundwater pumping threatens to deplete water, and climate change could exacerbate the problem.

“Water is at the heart for the past, present, and future of the Southwest,” he says. “We know it’s going to get hotter and drier, and that means, in some cases, that the springs in the Grand Canyon will begin to dry up because of the lack of moisture.”

Eberle said protecting the Colorado isn’t just for the people who live nearby, or the five million people who visit the Grand Canyon each year, or the more than 30 million people who depend on the river for water.

“It doesn’t matter whether you live in Arizona, New York, or Georgia, this national treasure belongs to you,” she says. “The national parks, and especially this one—as one of the most recognizable and iconic spots on Earth—belongs to each and every American, and every citizen of the world.”