Arizona's San Carlos Reservoir Nears Empty, Causing Massive Fish Kill

Arizona's San Carlos Reservoir is less than one percent full due to a historic lack of snow in the Gila River watershed. This extreme water depletion has led to a massive fish kill and an indefinite closure of the reservoir. The Gila River is a critical water source for communities, farms, and wildlife in the Southwest.

Winter snowpack in the Mogollon Mountains and Black Range typically replenishes the reservoir. In 2026, snowfall in the Gila River watershed was exceptionally scarce. Mountain snowpack reached only two percent of the 1991-2020 March median. Streamflow in April was 39 percent of normal levels.

By June, required water releases for downstream agriculture further reduced the reservoir's volume. It contained less than 400 acre-feet of water. Satellite images from the National Aeronautics and Space Administration (NASA) Earth Observatory illustrate this dramatic change. An image from May 22, 2026, shows the reservoir nearly empty, contrasting with its approximately 60 percent capacity in June 2023.

The dwindling water levels caused oxygen levels to drop sharply. This hypoxia resulted in the death of nearly all fish in the reservoir. Affected species included largemouth bass, black crappie, bluegill, channel catfish, flathead catfish, brown trout, and rainbow trout. Officials closed the reservoir indefinitely on June 5, 2026. The San Carlos Recreation and Wildlife Department warned of potential health risks from decomposing fish.

This is not the first time the San Carlos Reservoir has experienced severe low water. It has reportedly run dry at least 20 times since its creation in 1930. Previous major fish kills occurred in 1976 and 2018. The 1976 event killed over five million fish, requiring five years for the ecosystem to recover.

The region is currently in a multi-year dry spell, with much of the Gila River's headwaters experiencing severe drought. However, significant rainfall during the upcoming wet season could help replenish the reservoir. A National Oceanic and Atmospheric Administration (NOAA) seasonal monsoon outlook for May 2026 predicted a 33 to 50 percent chance of above-average summer rainfall. Strengthening El Niño conditions could also increase the likelihood of heavy rainfall in the U.S. Southwest.