A court battle over Colorado water could help determine how the American West responds to a shrinking river system, according to Inside Climate News.
The dispute centers on Denver Water's bid to expand Gross Reservoir to nearly three times its current capacity.
Critics contend the proposal reflects an older mindset in a region already pushing its water supplies to the limit.
Here's what to know
The case, before the 10th U.S. Circuit Court of Appeals, challenges the U.S. Army Corps of Engineers' approval of the reservoir expansion.
Environmental groups argue that the federal review did not seriously examine climate change, the Colorado River's overallocation, or whether enough water will exist to use the added storage, as Inside Climate News reported.
Denver Water wants to add 77,000 acre-feet of storage and says it would divert water from the Colorado River system in wetter years. The utility argues that the project could help protect about 1.5 million people from drought, wildfire disruptions and other emergencies.
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To the project's opponents, however, the stakes extend well beyond one reservoir.
A University of Colorado Boulder clinical law associate professor and the director of the Getches-Green Natural Resources, Energy, and Environmental Law Clinic, Sarah Matsumoto, said, "I just don't think it does anymore, without at minimum considering impacts of climate and impacts of overappropriation on the river."
Roughly 40 million people rely on the Colorado River.
More background
In 2024, a lower court ruled in favor of the environmental groups and found the review process inadequate.
As Inside Climate News relayed, Judge Christine Arguello wrote, "The cracked foundation of the Colorado River's management system all but demands skepticism over any proposal that will affect the hydrology of the Colorado River basin."
Work on the dam is nevertheless close to finished. An injunction issued in April 2025 halted construction, but part of that order was later lifted due to safety concerns about leaving the structure incomplete.
A separate restriction still prevents Denver Water from clearing forest below the dam or filling the newly added reservoir space.
The 1922 Colorado River Compact allocated more water than the river can reliably supply, and average flows since 2020 have stayed far below total allocations.
Approving additional diversions, critics say, could worsen shortages already affecting cities, farms, tribes and ecosystems.
Inside Climate News reported that William Eubanks, who represents the environmental groups, explained, "In effect, they're building a giant bathtub, even though there's likely no water to ever fill it."
If decisions continue to rely on older assumptions about water availability, the Colorado River's decline could leave communities tied to costly infrastructure that cannot deliver what it was meant to provide.
What's being done?
Denver Water says the expansion is a drought-planning measure, not an irresponsible push for more water.
Jessica Brody, general counsel for Denver Water, told the court that the utility has spent 23 years trying to correct an imbalance in its water system.
Beyond this dispute, the lawsuit lands amid a much larger basinwide reckoning. Colorado and the six other basin states are still negotiating how to reduce water use as the river continues to shrink, and experts say the case could shape how climate change is considered in future water infrastructure decisions.
It also reflects a shift in the West, where utilities are investing more in conservation, efficiency, and system upgrades rather than relying solely on larger dams and new diversions.
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