Dam it: 10th Circuit lets Denver Water complete Gross Reservoir expansion

The 10th Circuit vacated a lower court injunction that had barred Denver Water from filling its newly expanded Gross Reservoir, clearing the way to complete Colorado's largest dam project after more than two decades of planning and litigation. The court found the Army Corps of Engineers' environmental review was not arbitrary or capricious, reversing a 2024 finding by a district judge that it was.

The $600 million expansion, already physically completed in July, added 131 feet to the dam and 77,000 acre-feet of storage capacity, intended to serve 1.5 million people and shore up a northern water system currently reaching only 10% of customers. Environmental groups who sued in 2018 argued the permitting process lacked adequate review; the case now returns to the lower court with instructions to rule against them.

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