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View of the Colorado River from the Historic Navajo Bridge near Marble Canyon, Arizona.

Arizona relies heavily on the Colorado River, which analysts say is overallocated.

Yet Upper Basin states such as Colorado continue to look for ways to store water, and conservationists have filed suit to stop one such project.

Conservationists have long opposed expansion of a dam northwest of Denver that would divert an additional 5 billion gallons of water from the upper Colorado River watershed every year.

The coalition argues that the Army Corps of Engineers failed to consider that climate change would undermine the project, and that Denver, which has aggressively pursued conservation measures, doesn’t need the water.