It might seem like a profound ecological contradiction - deliberately poisoning a lake or river to make it better for fish.
But on a remote stretch of Montana ranchland owned by media mogul Ted Turner, along a peaceful tarn and meandering stream pressing up against the Spanish Peaks mountains, wildlife officials confront a piscatorial paradox.
The state of Montana wants to temporarily pollute 70 miles of the Cherry Creek drainage that runs through Mr. Turner's land into the Madison River. The goal, with Turner's blessing, is to kill thousands of exotic trout - rainbow, brook, and hybrid Yellowstone cutthroat - and replace them with imperiled westslope cutthroat trout and Arctic grayling.
Treating waterways with chemical toxicants to eradicate unwanted or ecologically damaging fish is part of a growing trend in landscape restoration pursued by wildlife managers nationwide.
From targeting sparkling waterways in the West "infested" with nonnative game fish planted earlier in this century to eliminating "rough fish" like carp and suckers from lakes in the East, the technique has produced undeniable environmental and financial success, proponents say.
Securing more habitat for westslope cutthroats in Montana, in this case by purging their chief competitors that can eat and interbreed with them, is considered the last best hope of staving off extinction and, more immediately, to keep these fish off the endangered species list.
First identified by explorers Lewis and Clark, westslope cutthroats have suffered severe declines. Only a few small genetically pure populations remain. The US Fish and Wildlife Service also ruled that Arctic grayling deserve to be federally protected, but intervention is delayed by the need to protect more-imperiled species.
Poisoning the waters of Cherry Creek has summoned controversy, amid allegations from critics that the poisons violate water-quality laws, pose potential threats to drinking-water supplies downstream, and represent an attempt to fix some problems best left alone.
"We feel man should not be going in there and attempting to play God," says William Fairhurst, a vocal critic of Montana's plan at Cherry Creek and former mayor of Three Forks, Mont. "We don't think this project is necessary and it is ill-advised to use poison. If you want to see what can go wrong, talk to the people who live near Lake Davis."
In recent months, state wildlife officials in California have endured severe public criticism for a botched attempt at eradicating exotic northern pike from a reservoir in northern California called Lake Davis. The 1997 action, designed to protect native salmon, failed to eliminate pike from the voluminous reservoir and set off outcries over unsubstantiated threats to drinking water.
Experts say what happened at Lake Davis is an exception and not comparable in scale or approach to the Montana plan.
The toxic agents generally deployed - rotenone and antimycin - choke out oxygen for only a short time and then break down quickly in the environment, says Calvin Kaya, an aquatic-ecology expert at Montana State University.
Rotenone entered the public lexicon in the 1950s as an agent used in the science fiction film "The Creature From the Black Lagoon." Derived from the root of a tropical plant, rotenone acts as fish toxicant by affecting the respiratory systems of fish and insects. It does not seem to affect birds or mammals, and ecosystems recovery quickly after use, studies show.
Many sport-fishing lakes across the country, threatened by carp and suckers stripping away aquatic vegetation, owe their health to chemical treatment.
At Knife Lake in Minnesota, a proposal to improve habitat for walleyes by first ridding the lake of carp with rotenone initially met with skepticism. A decade later, the lake ranks among top 10 walleye-fishing lakes in that angling-oriented state. A large-scale poisoning also was used to revive the sport fishery at Strawberry Reservoir in Utah.
"Chemically treating a lake is a profound action, but it's something you do when other tools in the ... box no longer work," says Tim Brastrap of the Minnesota Department of Natural Resources.
In the West, where several subspecies of trout are struggling, conservation efforts have intensified.
"Citizens anywhere else in the country would go ballistic if they were told to sit back and watch all their native whitetail deer or elk or moose or mallard ducks disappear," says Bruce Farling of the conservation group Trout Unlimited. "All we're suggesting is that in Montana and Idaho we don't want to see the same thing happen with this important native fish."
Rotenone and antimycin have been deployed to help golden trout in California, Apache trout in Arizona, Rio Grande cutthroat in New Mexico, and greenback cutthroat trout in Colorado. In each case, chemical treatment was used to kill rainbow trout to prevent interbreeding.
"I wish I could say we have a lot of time to address this problem, but we don't," says Pat Clancy of the Montana Department of Fish, Wildlife, and Parks. "We've already lost most of our populations, and in the habitat that remains, hybridization ... is a major concern."
Cherry Creek surfaced as a prime candidate for chemical treatment three years ago after a group of conservationists sued the Fish and Wildlife Service to have the westslope cutthroat listed as threatened.
To avoid listing a group representing environment, industry, and government interests devised a strategy to prevent extinction.
Native, genetically pure fish represent pinnacles of evolution, because they adapted to streams and survived centuries of change until humans began manipulating them.
Trying to turn back the clock
"Other states routinely use hatchery fish to provide opportunities for anglers at the expense of the wild fish that lived in the waters forever," Clancy says. "These decisions of the past, with introducing nonnative trout to Montana's waterways, are coming back to haunt us. We can't let our native species fall by the wayside."
Still, critics like Mr. Fairhurst see hypocrisy. "If a mining or logging company proposed dumping chemicals in a stream, they would be stopped in a heartbeat."
Last week, the Montana Department of Environmental Quality issued a report concluding that chemicals slated for Cherry Creek posed no threat to human health.
"It isn't a matter of playing God or not playing God. We've been playing God for a long time by disrupting the systems that nature gave to us. Our goal now is to turn back the clock, to repair the damage we've done."
(c) Copyright 1999. The Christian Science Publishing Society