UN 
As temperatures spike across the American Southwest this August, the future of water management on the Colorado River is being contested in a high-profile lawsuit unfolding in Santa Fe. The case pits the U.S. Army Corps of Engineers and Denver Water—the state’s largest utility—against a coalition of environmental organizations led by Western Resource Advocates.
At the center of the dispute is a proposed expansion of Gross Reservoir, which would allow Denver Water to divert an additional 18,000 acre-feet annually from the Colorado River Basin. Environmental groups argue that further withdrawals threaten the river system’s already precarious balance, exacerbated by ongoing drought conditions and record-low flows this season. Plaintiffs are urging the court to weigh climate science more heavily in federal permitting decisions, pointing to projections of up to 20% lower river flows by 2030 due to rising temperatures.
Denver Water maintains that the expansion is essential to ensure reliable supply for the region’s 1.5 million residents, especially during peak summer demand. The utility cites a $464 million investment in water efficiency and conservation measures, claiming that the reservoir project complements—not undermines—recent sustainability pledges. However, critics allege the utility’s climate adaptation plans do not account for cumulative ecosystem impacts, including on downstream states and tribal nations.
This legal battle is being closely watched ahead of the 2026 renegotiation of Colorado River water-sharing agreements among seven U.S. states and Mexico. With beaches along Lake Powell and Lake Mead receding to historic lows this month, the urgency for adaptive management is evident. The outcome of the Santa Fe lawsuit is expected to set a precedent for how climate risk is factored into large-scale infrastructure approvals in the region.
A decision from the U.S. District Court is anticipated later this summer, as regional policymakers and water managers look for signals on how climate priorities will shape Colorado River governance through 2026 and beyond.
Frequently Asked Questions
What is the Gross Reservoir expansion project by Denver Water?
The Gross Reservoir expansion project would allow Denver Water to divert an additional 18,000 acre-feet of water annually from the Colorado River Basin.
Why are environmental groups suing over the Gross Reservoir expansion?
Environmental groups are suing because they argue that increased withdrawals from the Colorado River threaten the river system, especially given projections of up to 20% lower flows by 2030 due to climate change.
Who are the main parties involved in the lawsuit over the Gross Reservoir expansion?
The lawsuit involves Denver Water and the U.S. Army Corps of Engineers as defendants, and a coalition of environmental organizations led by Western Resource Advocates as plaintiffs.
How does Denver Water justify the need for the reservoir expansion?
Denver Water claims the expansion is necessary to ensure a reliable water supply for 1.5 million residents and complements their $464 million investment in water efficiency and conservation.
When is a decision expected in the Gross Reservoir lawsuit, and why is it significant?
A decision from the U.S. District Court in Santa Fe is expected later this summer, and it is significant because it could set a precedent for how climate risk is considered in infrastructure approvals ahead of the 2026 Colorado River water-sharing renegotiations.
