In a significant ruling, a federal judge has ordered Denver Water to halt construction on the Gross Reservoir expansion project in Boulder County, Colorado. The decision comes after the U.S. Army Corps of Engineers was found to have violated multiple environmental laws during the permitting process.

The Gross Reservoir expansion, which aimed to triple the reservoir’s capacity, has been a contentious project since its inception. The plan involved raising the dam by over 100 feet, clearing 500,000 trees, and diverting water from local creeks. Environmental groups have long opposed the project, citing irreversible damage to ecosystems and wildlife.

Judge Christine Arguello issued a permanent injunction against the expansion, stating that the environmental harm caused by the project would be “irreparable.” The ruling also requires the Army Corps to rewrite key environmental documents and permits. Denver Water, which serves 1.5 million residents, has expressed its intent to appeal the decision, emphasizing the project’s importance for addressing future water shortages and emergencies.

The project, which began in 2022, was already 60% complete at the time of the ruling. A hearing is scheduled later this year to determine how to ensure the safety of the partially constructed dam.

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