The passage is about the history of the Tellico River in eastern Tennessee. The Tellico was devastated a century ago by commercial logging. Attempts to restore the habitat and the indigenous wildlife have met with mixed results. The river still holds trout, but they are mostly western rainbow trout, not native brook trout. The rainbows, which are not native to the east coast or the Appalachians are simply easier to breed, which is what the state wants. Fish that are easy to breed are easy to stock, and stocked fish generate income.
You can read the passage here, and you can find the book here.
I'm particularly happy with the photo here, because it's a photo of a free brook trout, one that is not attached to anyone's line, swimming away from me. It's hard to get such shots, but free-swimming brook trout really make me happy.