This weekend federal officials will begin another round of chemical treatments in the Colorado River meant to remove invasive fish.
But environmentalists want more to be done to protect native species.
On Saturday, biologists will begin using a piscicide called rotenone to try to remove predatory smallmouth bass below Glen Canyon Dam in order to protect the threatened humpback chub.
Conservationists say it’s a last resort in the absence of other steps not taken by U.S. Bureau of Reclamation to control invasive fish.
"That failure to act is, we think, now putting humpback chub in jeopardy, at very real risk of extinction," says Taylor McKinnon with the Center for Biological Diversity. "If we lose this source population, it’s sort of core, then we lose the motor for humpback chub recovery."
In recent years, Lake Powell’s plummeting levels have allowed warm-water invasive species like smallmouth bass and green sunfish to pass through Glen Canyon Dam.
McKinnon wants screens to be installed and river flows modified to stop their reproduction, along with other measures.
Smallmouth bass were discovered below the dam more than a year ago, but despite an earlier chemical treatment, their numbers have since more than doubled.
The fish are aggressive predators and have wiped out humpback chub populations elsewhere on the Colorado River.
