WASHINGTON — National environmental groups are declaring the Colorado "America's Most Endangered River," mostly because they say 110,000 gallons of contaminated water seep into it daily through radioactive uranium tailings near Moab.

"The Colorado River is not yet the most polluted river in the country, but it could become so if the current problems are allowed to fester," said Rebecca R. Wodder, president of the environmental group American Rivers.

It and partner groups — ranging from the Sierra Club to the Grand Canyon Trust and Friends of the Earth — each year release a list of America's most endangered rivers. They plan to formally release it this morning at the National Press Club.

The groups explained in advance that they put the Colorado atop this year's list largely out of worry that the Energy Department may not remove tailings from the old Atlas uranium mill site adjacent to the river and instead cap them in place.

"Someday a big flood like those that raged through these canyons in the 19th century is going to lift that pile into the river and irradiate Canyonlands National Park. It is pure folly not to move this pile away from the flood plain of the Colorado River," said John Weisheit with the environmental group Colorado Riverkeeper.

Bill Hedden, with the Grand Canyon Trust, added, "As long as this material remains on the riverbank, it poisons the river every day and threatens water supplies with catastrophic failure."

The Energy Department is scheduled to release next month a draft environmental impact statement that will identify a preferred option for handling the tailings. Utah politicians have vociferously opposed capping it on site — the cheapest alternative — as have California politicians worried about radiation in their downstream drinking water.

About 13,000 tons of uranium tailings are on 130 acres at the Atlas site. Interim remediation by the Energy Department now includes dewatering the tailings and pumping contaminated groundwater to an evaporation pond on top of the pile.

However, environmental groups say an estimated 110,000 gallons of contaminated water still seep into the river from the unlined pond every day — with contaminants including uranium, radium, ammonia, cadmium, arsenic, selenium and other heavy metals.