The Gila River is one of the Southwest’s most vital waterways, supplying water to communities, farms, and wildlife while connecting the snow-covered mountains of southwestern New Mexico with the desert landscapes of southwestern Arizona.
In years with ample precipitation, winter snow that accumulates in the Mogollon Mountains and Black Range provides much of the river’s spring runoff. That water helps replenish San Carlos Reservoir, which was created by the Coolidge Dam. When full, the reservoir ranks among Arizona’s largest lakes.
Snowpack Collapse Drains the Reservoir
Conditions were dramatically different in 2026. Snowfall in the Gila River watershed was exceptionally scarce, leaving mountain snowpack at just 2 percent of the 1991-2020 March median. As a result, streamflow during April reached only 39 percent of normal levels.
By June, required releases of water for downstream agricultural use had further reduced supplies. The reservoir contained less than 400 acre-feet of water.
A comparison of Landsat satellite images highlights the dramatic change. The image above (right), captured on May 22, 2026, shows San Carlos Reservoir holding only 389 acre-feet of water, making it less than 1 percent full. By contrast, the image on the left, taken in June 2023, shows the reservoir at roughly 60 percent capacity. Vegetation visible along the reservoir shoreline and river channel includes tamarisk, willow, cottonwood, sedges, and various grasses.
Massive Fish Kill Forces Closure
As water levels continued to fall, oxygen levels in the reservoir dropped sharply. The resulting hypoxia killed virtually all of the fish living there.
Officials responded by closing the reservoir indefinitely on June 5, 2026. Fish species affected included largemouth bass, black crappie, bluegill, channel catfish, flathead catfish, and stocked species such as brown trout and rainbow trout.
The San Carlos Recreation and Wildlife Department also warned that decomposing fish could create health risks for people attempting to fish or boat in the area.
A Long History of Extreme Low Water
Although the current situation is severe, it is not without precedent. News reports indicate that San Carlos Reservoir has completely run dry at least 20 times since it first filled in 1930.
Even during the original dedication of the dam and reservoir, conditions were dry enough for grass to grow across exposed lakebed. Humorist Will Rogers famously joked to President Calvin Coolidge: “If that was my lake, I’d mow it.”
Major fish kills have occurred before as well, including in 1976 and 2018. According to the Gila Herald, a fish kill in 1976 claimed more than 5 million fish, and the reservoir’s ecosystem required five years to recover.
Drought Continues but Rain Could Bring Relief
The region remains locked in a multi-year dry spell. Data from the U.S. Drought Monitor show that much of the Gila River’s headwaters in New Mexico is currently experiencing severe drought.
Still, the river’s flow can vary dramatically from year to year. Significant rainfall during the upcoming wet season could help replenish the reservoir.
A NOAA seasonal monsoon outlook issued in May 2026 estimated a 33 to 50 percent chance of above-average rainfall across the region during the summer. At the same time, El Niño conditions in the central and eastern equatorial Pacific were strengthening during late spring 2026, a pattern that can increase the likelihood of heavy rainfall across the U.S. Southwest.