The frog, a candidate for listing under the Endangered Species Act, is no longer found at Tamarack, Cagwin, Ralston, Lucille, Margery, Jabu and LeConte lakes in the wilderness area west of Lake Tahoe, biologists said.

They hope getting rid of non-native trout will restore the waters' once frog-friendly habitat, and the amphibians will make the leap from other areas in the nearby Eldorado National Forest.

Until the 1960s, the Sierra Nevada population of the mountain yellow-legged frog was prevalent throughout the northern and central Sierra. Since then, biologists estimate its population has declined by as much as 90 percent because of non-native fish stocking, disease, pollution and livestock grazing, U.S. Fish and Wildlife Service officials say.

Biologists say it takes up to four years for the mountain frog to complete its life stages from egg to tadpole to adulthood, which leaves it vulnerable to predators such as trout.

There were no fish in the seven alpine lakes before stocking of rainbow and brown trout to satisfy anglers began around 1950. Among the targeted lakes, the last fish planting was in 2000.

Sarah Muskopf, a Forest Service aquatic biologist, said field surveys indicate many of the fish already might have disappeared during the past eight years.

Muskopf added that other lakes in the wilderness area will continue to be stocked for recreational fishing.

The Forest Service is soliciting public comment on the plan through Aug. 22.