There was a bridge built over a waterway, yes, with a hard concrete channel underneath. Unless done absolutely correctly (and this is a very complicated subject

There was a bridge built over a waterway, yes, with a hard concrete channel underneath. Unless done absolutely correctly (and this is a very complicated subject of environmental science) the hard bottom channel can create erosion that destroys local riparian habitat within the erosion zone, as well as sedimentation that destroys (yes, destroys) downstream habitat. The increased sedimentation also changes the water chemistry and particulate content, so species of fish, insects (which fish, birds, and other animals eat, being an important base of the food chain), and other species are greatly affected, if not entirely killed off downstream. Of particular interest with this stream is salmon spawning, which is extremely sensitive and a huge focus of environmental groups in California and the northwest, for good reason. No one is simply claiming it—it is absolutely proven.