Denver Allowed to Repair Gross Dam After Court Blocked Expansion

Construction on a controversial dam outside of Denver is set to restart after a federal judge found there wouldn’t be additional environmental damage from conducting repairs while the city’s water authority completes a re-design.

The US District Court for the District of Colorado on Thursday vacated its previous order halting work on the Gross Dam, ruling that environmental groups didn’t show irreparable harm from the completion of the dam.

While Denver Water previously discharged dredged material into federal waters while tearing down the gravity dam, there is now “a risk of environmental injury and loss of human life if dam construction is halted for another two years while Denver Water re-designs the structure,” Judge Chrstine M. Arguello said.

Further, permanently blocking dam construction would require Denver Water to lay off “much of its specialized workforce” and interference with its contracts, causing the project’s costs to significantly increase, the opinion said.

Arguello ruled last year that the US Army Corps of Engineers erroneously approved the expansion of the Gross Dam reservoir, a project that would divert more water from the Colorado River to service the fast-growing Denver suburbs.

Save the Colorado, the Sierra Club, and other environmental groups asked the court to issue a permanent injunction against the dam expansion. But Arguello said in Thursday’s order that it allows Denver Water to ensure that the dam is structurally sound as the water authority commences a redesign process that can take up to two years to complete.

The groups are represented by Eubanks & Associates PLLC. The Corps is represented by the Justice Department. Denver—an intervening defendant—is represented by Crowell & Moring LLP, and the Office of the General Counsel for the Denver Water Department.

The Sierra Club has received funding from Bloomberg Philanthropies, the charitable organization founded by Michael Bloomberg. Bloomberg Law is operated by entities controlled by Michael Bloomberg.

The case is Save the Colo. v. Semonite, 2025 BL 186056, D. Colo., No. 1:18-cv-03258, 5/29/25.