The National Park Service will soon begin efforts to remove invasive smallmouth bass and green sunfish from the Colorado River below Glen Canyon Dam.
The non-native predatory fish were recently discovered breeding in areas where they hadn’t previously been found in large numbers and are posing a danger to the threatened humpback chub.
Smallmouth bass are aggressive predators and officials say failure to control their population in the Colorado River above the Grand Canyon would likely lead to the demise of the chub there.
Beginning Saturday, staff will use an Environmental Protection Agency-approved pesticide to kill the bass.
A second treatment could follow within two months. According to the Park Service, the fish piscicide rotenone used to eradicate the invasive fish is a natural substance derived from plant roots and has been effective in eliminating smallmouth bass elsewhere in the Colorado River Basin.
It’ll be applied to an area with dense vegetation at river mile -12 along with an impermeable fabric barrier at the mouth of the slough to minimize the exchange of water with the river.
The area below the dam will remain closed to the public during the work.
As water levels in Lake Powell have dropped to historically low levels this year, smallmouth bass and green sunfish have passed through the Glen Canyon Dam’s water intakes threatening the Grand Canyon and Glen Canyon Dam’s rainbow trout fishery below.