Low water levels below Glen Canyon Dam are now affecting trout health, the U.S. Bureau of Reclamation announced.

Lower water levels at Lake Powell and rising temperatures in the Colorado River are contributing to "dangerously low dissolved oxygen," the bureau said in a recent news release.

“Reclamation’s water quality forecasts suggested that there was potential for reaching low dissolved oxygen levels below the dam this year, but we didn’t anticipate it happening until early autumn,” Clarence Fullard, Reclamation fish biologist, said in the release.

On Aug. 16, the Department of the Interior announced 2023 operating conditions for Lake Powell and Lake Mead. The agency announced that there would be limited water releases from Lake Powell and Lake Mead in order to protect operational neutrality.                 

When the Bureau of Reclamation discusses dissolved oxygen, what they are referring to is the level of oxygen in the water that is available to fish and other organisms.

"A small amount of oxygen, up to about ten molecules of oxygen per million of water, is actually dissolved in water," the U.S. Geological Survey said. "Oxygen enters a stream mainly from the atmosphere and, in areas where groundwater discharge into streams is a large portion of streamflow, from groundwater discharge. This dissolved oxygen is breathed by fish and zooplankton and is needed by them to survive."

Dissolved oxygen is also important to the quality of the water.

Reduced oxygen in the water causes stress, increases metabolic rates and can ultimately result in fish kills or fish moving downstream to cooler, more oxygen-rich river habitats; the news release said. Reclamation and its partners continue to monitor temperature, dissolved oxygen levels and the health of fish in the area.

This is not the only fish-related challenge facing this portion of the Colorado River. Earlier this summer, juvenile smallmouth bass—a predatory fish not native to the area—were found in the river approximately two miles below the dam.