From this story in the Arizona Daily Sun:
An artificial flood in the Grand Canyon aimed at building sandbars to protect the endangered humpback chub has led instead to an eight-fold increase in the nonnative fish that is eating the chub -- the rainbow trout. So now, the federal Bureau of Reclamation is proposing to again kill thousands of trout using electroshock, perhaps annually for a span of a decade, and at a cost of millions of dollars to taxpayers. But at the same time, the bureau proposes more high-flow releases from Glen Canyon Dam, but this time paying closer attention to more than just how sandbars are built up.
_The flood of water from Glen Canyon Dam in 2008 was meant to build up sandbars for camping sites, protect archaeological resources and provide critical habitat for plants and animals, including the humpback chub. The unanticipated consequence was that the flood cleared the gravel floor just below the dam where rainbow trout lay their nests. As the fish grew, they found themselves competing for limited food, and some moved downstream to fight for the same resources as the humpback chub at the confluence of the Little Colorado and Colorado rivers, said Melis. The rainbow trout that had been declining in numbers since 2001 in the Colorado River rose by 800 percent between 2007 and 2009, he said. The increase followed efforts to remove more than 23,000 rainbow trout from areas where humpback chub thrive. "This (flood) might have been just the right thing and the right time to turn that (trout) population upward," Melis said. "That's a good thing for the sport fishermen, but when they start moving downstream and start interacting with humpback chub, that's where the concern is."