The Colorado River has been called the American West’s hardest-working river. Lately, it’s been earning overtime.
The river supplies water to some of the country’s largest cities, including Los Angeles and Las Vegas, as well as its most fertile swath of farmland, California’s Imperial Valley. Forty million people in seven states rely on the Colorado every day, and each year six million more visit its most magnificent stretch, the Grand Canyon.
But many non-human creatures also depend on the Colorado watershed, most of all the strange, hardy fish that prowl its turbid depths. This is the domain of the bonytail chub, the razorback sucker, and the Colorado pikeminnow, a six-foot-long predator that early anglers caught by tying fishing lines to their truck bumpers. The lower Colorado has the highest ratio of endemic fish in North America—meaning that six of its eight native species exist nowhere else on Earth.
The best-studied member of the river’s distinctive ecosystem is the humpback chub, a creature as bizarre as fish come. Gila cypha is a silvery, foot-long member of the minnow family that has big orange fins and a fleshy, ridge-like protuberance along its back—its mysterious hump. If you crossed a carp with a bison, the humpback chub is what you’d get.
“They’re a unique part of the Grand Canyon, just like the rocks and the springs and everything else that makes this place special,” says Brian Healy, lead fish biologist for Grand Canyon National Park. “They evolved here over millions of years.” During the 1800s, one gold prospector in the canyon reported that you “could pull them out by the tail two at a time.”
The 20th century, however, wasn’t kind to the humpback chub. Fisheries managers stocked non-native trout and bass and encouraged fishermen to kill chub and other “trash fish,” so-called because of their perceived lack of value as sportfish. Gargantuan federal dams, such as the Hoover Dam, the country’s largest, drowned many of the fast, rocky river stretches that chub need to survive. In 1967 the government declared the chub an endangered species, a measure that failed to halt its spiral toward extinction.div">>Please be respectful of copyright. Unauthorized use is prohibited.Please be respectful of copyright. Unauthorized use is prohibited.
Left: Humpback chub swim underneath a waterfall on the Little Colorado River.
Right: After measuring humpback chub, U.S. Fish and Wildlife Service biologist Randy Van Haverbeke releases a net full of the fish into the Little Colorado River during the agency's annual survey of the species. The biologists and the photographers used the same bait to draw in the humpback chub.Photograph by David Herasimtschuk / Freshwaters Illustrated
But in recent years, chub numbers have begun to tick upward again, thanks partly to conservation efforts, such as translocating fish into productive tributaries unblemished by dams. Some 12,000 adult chub now live in the Grand Canyon stretch of the Colorado, and several thousand more are scattered across four populations upriver.
In a 2018 study, the Fish & Wildlife Service found that the humpback chub had improved enough to qualify as a threatened species, meaning it was no longer at imminent risk of extinction. i">>(Read how the Grand Canyon stretch of the Colorado River is one of the most endangered in the U.S.)
After three years of review, the agency finalized that rule on October 15. It has also proposed taking the same action for the razorback sucker, listed as endangered since 1991. Together these rulings suggest that the Colorado River’s beleaguered ecosystem is heading in the right direction, validating decades of research and conservation.
Yet the chub’s future isn’t secure. The federal government recently declared the Colorado Basin’s first-ever water shortage, triggering cuts for certain states, such as Arizona—even as others, such as Utah, explore the possibility of using more. According to one projection, climate change could cut the Colorado’s flows in half by century’s end. i">>(Read more about the megadrought that has hit the U.S. water supply.)
“It’s still a precarious picture for the humpback chub,” says Taylor McKinnon, senior public lands campaigner at the Center for Biological Diversity, a nonprofit based in Arizona. “I’m far from convinced that it’s out of the woods.”
How the humpback chub was dammed
Before humans intervened, the Colorado River was prone to wild fluctuations, from a raging torrent during spring run-off to a trickle in summer. Some 65 million tons of sediment—the liquefied stuff of the West’s mountains and deserts—flowed through the Grand Canyon each year. The humpback chub evolved to thrive in this volatile environment, in part, many scientists believe, because of its namesake hump. Some suggest that the bulge acts as a keel-like stabilizer, steadying chub during spring floods. Others hypothesize that it makes the fish harder for predatory pikeminnows to gulp down.
Beginning in the 1930s, dams altered the river. A series of massive concrete walls—designed to control floods, store water, and churn out hydroelectricity—cleaved the Colorado into a chain of sluggish reservoirs unfit for chub, which prefer swift currents and spawn in rocky-bottomed stretches of river. The Hoover Dam, which straddles the border between Nevada and Arizona, and the Flaming Gorge Dam, in Utah, wiped out nearby populations. i">>(Read how scientists are saving the Colorado, one habitat at a time.)div">>