Wilderness workers are recruiting beavers for habitat restoration. Beavers are a keystone species for two reasons. First, they're fussy about water quality: if you have beavers, then you know that your water is pretty good. Second, they have a huge impact on the whole ecosystem around them. By damming creeks, they create ponds that establish habitat for many more creatures than a small trickle would offer. Just putting back the beavers that have been extirpated from many places can go a long way toward fixing the damage.