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. …