The National Park Service announced that are removing some invasive fish that are threatening another native fishing species from the Colorado River below the Glen Canyon Dam.
The agency said they are removing smallmouth bass and green sunfish, which are "threatening the recovery of humpback chub" who are protected under the Endangered Species Act.
"These non-native predatory fish were recently discovered breeding in areas where they have not previously been found in large numbers," the agency said. "Because smallmouth bass are aggressive predators, failure to quickly control their population in the Colorado River above the Grand Canyon could likely lead to the demise of the humpback chub."
The agency said the invasive fish will be killed by use of "EPA-approved fish piscicide rotenone (CFT legumine)."
"Threats to native fish are increasing due to the warmer temperatures of water passing through the dam and related increased river temperatures below the dam, which increase non-native fish spawning and reproduction, and allow for predation on native fish populations downriver. Juvenile smallmouth bass were found in the Colorado River below Glen Canyon Dam on July 1, underscoring the urgency of this emergent issue," the agency said.
The agency said the first treatment was used Saturday and Sunday.
A second treatment might be used within two months if necessary, the agency said.
Park service officials said the area being treated will be closed to the public, but the river itself will not be closed.