Grand Canyon Fish Invasion Prevented

An invasive fish has been stopped from taking over the Grand Canyon in an ingenious way.
These invasive smallmouth bass are from the eastern and central United States and threaten native species in the Colorado River, including the humpback chub.
To slow their spread, the U.S. Bureau of Reclamation has started releasing cold water from Lake Powell out of the Glen Canyon Dam, cooling the waters in the Grand Canyon and making them less habitable for the invasive fish.
Smallmouth bass have plagued the upper Colorado River Basin for decades, impacting numerous native fish species, but were only detected downstream of the Glen Canyon Dam in 2022.
Smallmouth bass are effective predators and compete aggressively for food resources, preying on young native fish. Species at risk include the humpback chub, 90 percent of which live within the Grand Canyon.
“These non-native predatory fish were recently discovered breeding in areas where they have not previously been found in large numbers, threatening the recovery of humpback chub, which is listed as threatened under the Endangered Species Act,” the National Park Service said in a statement last summer.
After the smallmouth bass were detected downstream of the Glen Canyon Dam, officials feared they would start to breed and spread irreversibly throughout this section of the river. To prevent this, they decided to forcibly cool down the Colorado River by releasing water from Lake Powell, bringing temperatures below the 60 degrees Fahrenheit needed for the smallmouth bass to breed.
“Cool temperatures of less than 15.5 degrees Celsius (60 degrees Fahrenheit) year-round are expected to lead to minimal to no initiation of spawning in smallmouth bass and possibly other species, such as green sunfish, as well as poor growth and survival of early life stages,” the Bureau of Reclamation explained in a report earlier this year.
This plan was implemented in early July, and according to officials, it appears to be working. The Bureau of Reclamation revealed last week that electrofishing, netting, and snorkeling efforts have all revealed no newly hatched bass, The Arizona Republic reported.
“That’s huge,” Kelly Burke, executive director at Wild Arizona and its Grand Canyon Wildlands Council, told the outlet. “It couldn’t be better timed. We’re having an extraordinarily hot summer.”
This success also means that the National Park Service will not dump rotenone, a fish-killing chemical, into the river as it did last August.
Despite this win, there are still concerns that the smallmouth bass will continue to enter the lower Colorado River via the Glen Canyon Dam’s hydroelectric turbines. Additionally, releasing colder water from Lake Powell’s depths means that this water lowers the levels of the already dwindling reservoir, all without providing hydroelectric power to the millions of people depending on it nearby.
“Status-quo electricity production at Glen Canyon Dam will continue the inundation of predatory bass into the Colorado River, almost surely driving the Grand Canyon’s endangered humpback chub to extinction,” Taylor McKinnon of the Center for Biological Diversity said in a statement earlier this year.
“The agency needs to screen the dam to stop bass from entering the Grand Canyon in the first place, which it’s been promising but failing to do for eight years. Climate change is drying up the Colorado River, and deadpool at Glen Canyon Dam is inevitable. The Bureau of Reclamation must stop burying its head in the sand and develop a robust plan for navigating that in a way that protects the Grand Canyon’s endangered native fish.”
The Arizona Republic reports that the Bureau of Reclamation and National Park Service are indeed considering some form of barrier to the fish’s movement and a number of other measures to prevent smallmouth bass from entering the lower Colorado River.
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