More than a century ago President Theodore Roosevelt created Grand Canyon National Monument, calling the vast chasm “the one great sight which every American should see.”

Today the iconic landmark has national park status, and the protected area has expanded to encompass the entire 277-mile formation. But for Arizona’s indigenous tribes, such as the Havasupai and Navajo, that’s not enough. They’re seeking to protect 1.7 million acres surrounding the canyon to keep uranium mining from threatening the purity of their water. Advocates are pushing President Barack Obama to create the Greater Grand Canyon Heritage National Monument and permanently put an end to new mining claims in the locale.

This isn’t the first time the Grand Canyon has faced the threat of development, and it certainly won’t be the last. The breathtaking layers of sandstone, shale, and limestone that draw millions of visitors to the park each year also hide rich veins of uranium and other precious minerals. In 2007 ore prices soared and four previously closed mines were reopened. With three of the mines still operating in the canyon’s watershed, area communities fear that their scant resources are slowly being poisoned.

The mining companies contend that any possible contamination would never reach the park. But in 2010 the U.S. Geological Survey found that 15 springs and five wells just outside the park’s boundaries had uranium concentrations in excess of federal drinking water standards. The National Park Service, in turn, says it’s concerned by the lack of monitoring for groundwater contamination by the industry.

Four years ago the Interior Department banned new uranium mining on 1 million federal acres over a two-decade span. The National Mining Association appealed that order; the case is still making its way through the courts. But a new national monument would make the ban more bulletproof, and so seven tribes have united with environmentalists and a U.S. representative from Arizona to support it.

“We’re seeing a legacy of industry benefiting at the expense of the canyon,” says Anne Moriah Tapp, the energy program director of the Grand Canyon Trust. “There is a lot of risk at stake in one of the greatest resources in the world.” It’s now up to another president to save it.