EDIT: Oh, this really pisses me off. I just got done reading some Yahoo! article about the deterioration of the environment in the Grand Canyon. In this article, they mention problems with exotic invaders like salt cedar, Asian tapeworms, and trout. The Glen Canyon dam has also royally screwed the area for several reasons. First, the usual ebbs and floods are gone, cutting out natural variation. Second, water holds more sediment when it runs fast. The Glen Canyon dam backlogs all that water upstream, which causes its sediment load to settle out and clog up the forebay. Then, because the water released out of the dam is sediment-free (and colder), it runs faster and erodes more than it out to. This is not rocket science. This is Geology 101.
But what really makes me want to freak out is the trout issue. Four out of eight native fish species in the Canyon have gone extinct. Number five, the humpbacked chub, is on the way. One of the problems for the crub is that the unusually cold and clear water makes reproduction difficult (the Colorado is naturally warm and muddy). The second problem is that the exotic trout eat young chub. But the kicker is that they aren't acting to remove the exotic trout, because the fishermen protest.
That is one of the most irresponsible perspectives in natural resource management; to preserve (or create) recreational opportunities at the DIRECT expense of nature. Guess what: fishing for exotic trout in the Grand Canyon is not a God-given priviledge. Neither do we need to keep Lake Powell to preserve the waterski and jetski industry. There are more important things. Go buy some trout smelt and stock a kiddie pool in your backyard. Trout are not on the verge of extinction. Spending time fishing in the Canyon is not worth the existence of an entire species.