It may seem counterintuitive, but wolves can actually help the environment.
As Sustainable Man explains, when wolves were unnaturally removed from Yellow Stone park, the environment became heavily unbalanced. The deer had no natural predators, and, as a result, over ate the greenery. The ended up hurting the entire ecosystem.
When the wolves were recently reintroduced, nature became balanced again. The wolves had such a positive chain reaction effect, their presence ended up changing the rivers for the better.