Halted dam releases threaten Colorado River ecosystems

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By Erik Stokstad, Science. 

Excerpt: In 2024, the U.S. Bureau of Reclamation (USBR) opened outlets at the base of the Colorado River’s mighty Glen Canyon Dam, unleashing gushers of water in an experiment meant to cool waters downstream. The strategy, called a “cool mix” release, aimed to thwart breeding of invasive smallmouth bass and protect native species. “It was very effective,” says Kevin Bestgen, a fish biologist at Colorado State University. So much so that the release was repeated in 2025. But with the Colorado’s reservoirs at historically low levels, there may be little political will to release water to protect ecosystems. On 6 August, USBR, which operates dams on the river, canceled this year’s cool mix release. In April, the agency had also nixed one of the periodic “controlled floods,” a much larger cascade intended to redistribute sediment and build sandbars that provide habitat for fish. ...The developments are the latest sign of trouble on the river system, which supplies water for 40 million people across seven states. This year saw record low snowpack levels in the Rocky Mountains, which means less water flowing downstream into the two largest reservoirs in North America: Lake Powell behind the Glen Canyon Dam and, farther down, Lake Mead behind the Hoover Dam.... 

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