Biologists are preparing to poison off all the fish in a stream in Yellowstone National Park ahead of an effort to restore native fish species to those waters.
Nonnative brown and rainbow trout have invaded and become established in Grayling Creek and its tributaries north of West Yellowstone, Mont.
This week, biologists plan to put small quantities of a toxin in the streams to kill off the nonnative trout. Treatments with the chemical Rotenone will continue for two to three years until all of the nonnative fish species are gone.
After that, biologists plan to restock the creek drainage with two native species, Arctic grayling and westslope cutthroat trout.
Yellowstone officials say people shouldn't swim or drink from the streams through Aug. 30.