Court Rules Feds and Denver Water Can Proceed With Gross Reservoir Expansion

September 17, 2026 at 02:53 AM2 min

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The 10th Circuit Court of Appeals ruled Tuesday that the U.S. Army Corps of Engineers and Denver Water may proceed with the Gross Reservoir expansion near Denver. The ruling overturns a lower court decision that had halted construction. The project would add 77,000 acre-feet of storage, enough to supply roughly 150,000 homes.

Key Facts

The 10th Circuit Court of Appeals ruled Tuesday in favor of the U.S. Army Corps of Engineers and Denver Water, allowing the Gross Reservoir expansion to proceed.
The expansion would add 77,000 acre-feet of water storage, enough to supply roughly 150,000 homes.
Save The Colorado, the environmental group that sued to halt the project, said it will not appeal the decision.
The project involves raising the dam by 131 feet, tripling the reservoir's capacity.
Denver Water serves 1.5 million people and says the expansion is vital for a secure water supply amid drought and wildfire risks.

Court Ruling

The 10th Circuit Court of Appeals ruled Tuesday that the U.S. Army Corps of Engineers and Denver Water may proceed with the Gross Reservoir expansion near Denver. The ruling overturns a lower court decision that had halted construction. Save The Colorado, the environmental group that challenged the project, said it will not appeal the decision. Gary Wockner, director of Save The Colorado, said the ruling is 'nonsensical' given the Colorado River's stress from climate change.

Project Details

The expansion would raise the dam by 131 feet, tripling the reservoir's capacity. The additional storage would hold 77,000 acre-feet of water diverted from the Colorado River, enough to supply roughly 150,000 homes. Denver Water began planning the expansion after the severe drought of 2002, but construction did not start until April 2022. The utility says it has exhausted water efficiency options and the expansion is the only way to reduce drought risk for the 1.5 million people it serves.

Colorado River Concerns

Environmental groups argued the expansion would allow Denver Water to pull more water from the Colorado River, which supplies 40 million people across seven Western states and Mexico. Save The Colorado said the Corps did not fully account for the dam's impacts on the river system already stressed by climate change. Denver Water said the expanded reservoir is vital for managing constrained water supplies amid growing risks of wildfire and weather extremes.