Chemical Rotenone in Colorado River Possible Solution to Invasive Predatory Fish Smallmouth Bass

Rotenone, an FDA-approved chemical, will be used by authorities to treat the Colorado River in an effort to eradicate populations of invasive predatory fish, such as smallmouth bass and green sunfish.

Chemical Rotenone in Colorado River

The National Park Service announced Friday that it would redouble its attempts to kill invasive fish with a chemical treatment in a section of the Colorado River in northern Arizona.

Rotenone, a drug that is fatal to fish but has been authorized by federal environmental inspectors, will be released starting on August 26.

It's the most recent move in an ongoing battle to safeguard a threatened native fish, the humpback chub, and keep non-native smallmouth bass as well as green sunfish away below the Glen Canyon Dam.

The Colorado River slough, a cobble bar region surrounding the backwaters where the smallmouth bass was discovered, and a little length up and downstream will need to be closed during the course of the weekend as part of the treatment.

Last year, chemical compounds were also used.

The National Park Service promised the public that the effort would be carefully planned and carried out to minimize human exposure to the chemical as well as desired fish species.

At the slough's mouth, an impermeable fabric wall will be built to stop water from entering the river.

The park service stated that after the treatment is finished, a different chemical would be discharged to dilute the rotenone.

Smallmouth Bass

Smallmouth bass had previously been isolated in Lake Powell by the Glen Canyon Dam, which had acted as a barrier to them for many years.

However, they were discovered in the river beneath the dam last summer.

Lake Powell, a significant reservoir on the Colorado River, plummeted to record low levels last year as a result of climate change and persistent drought, lessening its significance as a barrier for smallmouth bass.

The Grand Canyon is home to the largest populations of the extinct and rare humpback chub, and the predatory fish were able to get there.

Environmentalists have charged that the federal government has been slow to act.

The Center for Biological Diversity cited National Park Service data released on Wednesday, which showed that the number of smallmouth bass had more than doubled in the previous 12 months.

The group also claimed that no timetables for changing the region below the dam had yet been provided.

Also Read: 5 Invasive Fish in NC Listed by Officials Under Aquatic Nuisance Species (2023)

Humpback Chub

The Grand Canyon may experience an entirely preventable extinction event, according to Taylor McKinnon, the Center's Southwest director.

The entire species is in danger if the humpback chub's core population disappears.

Additionally, environmental advocacy groups are still upset about the 2021 decision to reduce the humpback chub from endangered to threatened status.

Federal officials declared that the fish, which derives its name from a fleshy hump behind its head, had been saved from extinction following decades of protection at the time.

The Colorado River's native, endangered humpback chub fish first appeared about 3 to 5 million years ago.

By most standards, the humpback chub is a small fish, growing to a maximum size of around 20 inches and 2.5 pounds.