Yes, a complete local ecosystem has taken a big hit there. The whole system has been temporarily unbalanced and other species will suffer too, not just the fish.
Yes. A loooooong while.
But, at the same time. Events like this that push an ecosystem to its limits, also help to reset the invasions from over competitive, non-native species. It also helps the aquatic populations with local adaptations re-establish themselves and get a foothold again.