The Wayne N. Aspinall Unit, Colorado’s only stake in a federal hydropower system that sells power across the West, is on pace to generate nearly 30 percent less electricity than its historical average dating to 1978, according to the Bureau of Reclamation. The shortfall is the latest sign of a decades-long decline eroding a system that accounts for about 3 percent of Colorado’s energy supply.

The unit’s three dams on the Gunnison River — including Blue Mesa, Morrow Point and Crystal — make up Colorado’s only piece of the Colorado River Storage Project, a Depression-era network of federal dams selling power to municipalities, cooperatives, tribes and irrigation districts across the West. Blue Mesa Reservoir, the largest body of water entirely within Colorado, is expected to end the year at just 17 percent of its live storage capacity.

As the river shrinks under the stresses of climate change, so does the unit’s output. And the electricity that the waterway does not help to generate has to come from somewhere else, usually at a higher price.