Denver’s Gross Reservoir expansion violates Clean Water Act, federal judge rules

Denver Water’s permit from the U.S. Army Corps of Engineers for the ongoing expansion of Gross Reservoir violates the Clean Water Act and the National Environmental Policy Act, according to a ruling Wednesday from a U.S. District Court judge. 

Senior federal judge Christine Arguello did not order Denver Water to stop construction in Boulder County, which has been underway since 2022, but said the environmental plaintiffs have a right to relief from any damage that will occur to surrounding land and forest once the dam closes and the expanded pool rises. 

“To the extent Denver Water disagrees, it has only itself to blame — because Denver Water chose to proceed with construction despite the obvious risk posed by pending federal litigation,” according to the ruling, in the U.S. District Court for Colorado. 

Arguello ordered Denver Water to start talks with the plaintiffs, including Save the Colorado, the Sierra Club, WildEarth Guardians and others, on how to “remedy” the Corp’s violations of the key environmental laws. 

Denver Water was preparing a statement reacting to the ruling Thursday afternoon. 

“It’s huge. Put that in capital letters,” said Save the Colorado founder Gary Wockner in an interview. “It’s a stunning victory for the Colorado River, for the people of Boulder County and Grand County,” Wockner said. “Boulder County, because of where this massive project was being built, and in Grand County, because their rivers were going to be further drained. And it’s a victory for the rule of law.”

The plaintiffs were still reading the 86-page ruling and have not had time to confer on whether to seek an injunction against further construction at Gross Reservoir, or what environmental mitigations they might seek in conference with Denver Water, Wockner said.

Save the Colorado and various coalition partners have had success slowing or stopping dam and river alteration projects, as part of their mission to halt further diversions of western-flowing Colorado River water to Front Range water agencies and to leave more in the rivers for wildlife. Wockner noted Thursday that they have also sued over permits for the sprawling $2 billion Northern Water effort called Northern Integrated Supply Project. 

“Court precedents matter,” Wockner said, pointing to the potential impact of the Gross Reservoir ruling. 

The judge said the parties should file briefs on their positions if they don’t reach an agreement by Nov. 15. 

“It is ordered that counsel for all parties shall confer and attempt in good faith to reach an agreement as to remedies concerning the issues on which the Corps was not in compliance,” Arguello wrote. 

This is a developing story and will be updated.