SACRAMENTO, California — The U.S. Forest Service on Wednesday rejected environmentalists' appeal of a plan to poison a stream south of Lake Tahoe to aid what wildlife officials call "the rarest trout in America."

Unless opponents sue, the decision frees the California Department of Fish and Game to seek a permit to clear nonnative fish from 11 miles of Silver King Creek next month using rotenone, a toxic chemical.

The department then wants to restore the Paiute cutthroat trout to its native habitat in the Carson-Iceberg Wilderness. Silver King Creek flows into the Carson River south of Lake Tahoe.

The trout evolved into a separate species after it was cut off from other waterways about 5,000 years ago, though populations have since been transplanted into four other Sierra Nevada waterways.

Restoring the fish to the 11 miles of Silver King Creek may lead to ending the trout's listing as a threatened species, wildlife officials said.

The department had hoped to act last year, but was delayed by an environmental lawsuit that forced the Forest Service to prepare an independent environmental analysis. The appeal focused on the service's finding that the poisoning wouldn't seriously affect other species, particularly the water insects that fish eat.

"Essentially what they're proposing is to kill everything — everything — in this stream. Some of these things are very difficult to reintroduce," said Patty Clary, executive director of Californians for Alternatives to Toxics.

Wildlife officials said insects and other species wiped out by the fish poison are likely to repopulate the creek within a couple of years.

The department is considering using the same chemical to try to wipe out voracious foreign northern pike in Lake Davis, north of Lake Tahoe.