Occasionally in science, there are clear causal pathways. We know, for example, what wolves hunt and we can calculate how many elk are in the park. While some scientific questions are cut and dry, most are nuanced. In ecology, there are thousands of species in a given habitat, all exerting force on each other. Additionally, outside forces play a role, be they habitat destruction, highway placement, or pollution. So yes: wolves do change rivers. But it is unlikely that they are the only force changing them. Instead, they are part of a complex web of ecological goodness, making the habitat healthier for all.