Determined to find out exactly why, Abraham Karam, a young biologist working for Marsh, implanted acoustic transmitters in 20 hatchery fish and released them into the lake in 2006. The fish averaged 15 inches in length, the standard size they reach in one to two years at Willow Beach. Within less than six months, 16 of the transmitters had stopped moving, meaning the fish were dead. Another one of Marsh's biologists, Brian Kesner, recovered 13 transmitters by diving to the lake floor.

Karam's research fingers striped bass, the only fish whose mouths can open wide enough to munch 15-inch-long prey. (A subsequent study involving razorbacks 19 inches and longer found that the larger fish survive better.) He's convinced that the stripers, which were initially stocked in Lake Mead but spilled over the Hoover Dam during a high-water year in the early 1980s, are flourishing in Lake Mohave thanks to a nearly unlimited food supply: stocked rainbow trout. Well-fed, the bass have become formidable. Anglers regularly reel 40-pound stripers from the lake, and Nevada's record-setter, weighing 60 pounds, was caught on Mohave in 1998. Now, these colossal fish are devouring the hatchery-raised razorbacks -- along with bonytails, an even more perilously endangered native fish.

Karam is amassing additional evidence from Mohave fishermen. One angler found an acoustic transmitter -- one of those lost in Karam's study -- in the stomach of a striped bass caught just a couple of miles from where the tagged fish were released.

Others have noted the problem. On an online message board run by a popular lure company -- one striped bass model they sell is called "hatchery trout" -- a die-hard bass fisherman recently wrote, "For the green people who spend all of our tax money raising suckers, I have a word for them: The lake is full of predators and they are eating machines. When you stock suckers, the predators come from far and wide and go on a feeding spree. They eat all of your hard work raising suckers. Doesn't that register with you?"

An alphabet soup of conservation and recovery plans has been created to protect the razorback sucker. In the Lower Basin, the fish is part of a federal conservation plan, a $626 million, 50-year, 43-species effort launched in 2005. In the Upper Basin, more than $120 million in federal funds has already been spent on razorback sucker recovery efforts. According to some estimates, an additional $84 million could be spent by 2023.

On the upper river -- much of which still resembles a river -- the initial recovery projects focused mainly on improving and regenerating habitat: regulating flows, simulating floods, restoring gravel bars. Those efforts have been largely fruitless. "You'd like to see more fish in a bigger range," said Harold Tyus, a University of Colorado at Boulder professor who wrote the recovery plan for the razorback sucker while working for the U.S. Fish and Wildlife Service. "What are we seeing? Less fish and in a smaller range."

Some Upper Basin watchers see the story as one of missed opportunity, in which state officials continued to stock non-native fish long after they should have known better. The state of Colorado, for instance, stocked largemouth bass in the Elkhead Reservoir, near the town of Craig. Despite screens intended to prevent the fish from escaping, they've spilled over the dam and now dominate some stretches of the Yampa, a tributary that flows through the northwestern part of the state.

Which brings us to the built-in, largely intractable problem that looms over native fish recovery efforts: State wildlife agencies, which cooperate with the federal government on endangered species recovery, derive their revenue from recreational fishing. As Tyus put it, "The very agencies you're dependent on to recover the fish are the very agencies that are responsible for their plight."

Because sport fishing is big business -- for the agencies as well as local economies -- it's likely here to stay. People who enjoy catching rainbow trout and striped bass and other species that didn't evolve in the Colorado River ecosystem are not about to give up their right to do so. (Marsh impishly pointed out that Burke likes to catch stripers on Lake Mohave, sometimes delivering filets to Marsh's camp during the Roundup.) Halversson, in his book, cites a 2005 Fish and Wildlife Service economic analysis of stocking programs: Every dollar spent growing and stocking rainbow trout led to $32 of economic activity.

Angela Kantola, assistant director of the Upper Colorado River Endangered Fish Recovery Program for the Fish and Wildlife Service, said the states have greatly improved their fish-stocking practices in recent decades. "The problem isn't stocking the fish," she said.  "It's controlling the fish that are already in the system." In the Upper Basin, said Kantola, recovery agreements now prevent states from stocking sport fish where they'll be harmful to native fish, but she acknowledged that the states' dual roles "require some give and take, and some continued research."

So the turf wars continue -- and stretch far beyond feuds between sport-fishing advocates and native species conservationists. Within the conservation community, antagonism and lack of cooperation between the Upper and Lower basins shadows the future of the razorback sucker and its fellow endangered fishes. Lower Basin advocates are wont to complain that the Upper Basin has gotten most of the money -- oversight for native fish recovery on the entire Colorado lies with the Fish and Wildlife Service's Denver office -- and wasted it on habitat restoration when the real problem was non-natives.