San Carlos Reservoir in Arizona has become a stark snapshot of what drought can do when snowpack fails, water demand continues, and summer heat closes in. New NASA Earth Observatory images show the reservoir nearly empty in May 2026, with only 389 acre-feet of water left, which is about 127 million gallons and less than 1% of its capacity.
The result was not just a smaller lake. Officials closed the reservoir indefinitely on June 5, 2026, after low water helped create hypoxia, a dangerous drop in oxygen that killed virtually all of the fish living there. For anglers, nearby communities, and wildlife, the lake’s collapse is the kind of event that turns a dry spell into an ecological emergency.
A river under pressure
The Gila River is one of the Southwest’s important water routes, carrying water from snow-fed mountains in southwestern New Mexico toward the desert lowlands of Arizona. In good years, snowmelt from the Mogollon Mountains and Black Range helps refill San Carlos Reservoir, which is formed by Coolidge Dam.
However, 2026 was not a good year. NASA reported that snowpack in the Gila River watershed was only 2% of the 1991 to 2020 March median, and April streamflow reached just 39% of normal. That is a thin margin for a reservoir expected to support farms, people, and wildlife.
By June, after mandatory water releases for downstream agriculture, less than 400 acre-feet remained. This means a reservoir that looked broad and blue in June 2023 had been reduced to exposed river channels, scattered green vegetation, and warm shallow water by May 2026.
NASA’s two-frame warning
The contrast NASA published is easy to understand, even for someone who has never visited the lake. A Landsat image from June 7, 2023, shows San Carlos Reservoir at about 60% full, still looking like one of Arizona’s largest bodies of water.
A second Landsat image, captured on May 22, 2026, tells a very different story. The reservoir was nearly empty, and the Gila River’s natural channel had become visible again. Along the exposed edges, NASA identified plants such as tamarisk, willow, cottonwood, sedges, and grasses.
It is a simple before-and-after scene, but the message is not small. When a reservoir shrinks this far, it stops acting like a stable lake and starts behaving more like a stressed, overheated basin where oxygen can disappear fast.
Why the fish died
Fish need dissolved oxygen in the water. When water levels fall sharply, the remaining water can warm more quickly, become stagnant, and lose the conditions many fish need to survive.
That is where hypoxia comes in. NASA said declining water levels contributed to low oxygen conditions that killed virtually all fish in the reservoir, including largemouth bass, black crappie, bluegill, channel catfish, flathead catfish, brown trout, and rainbow trout.
