I was having the same problem as well. I had to restart the mission 4 times. But I think I may have found a solution.
For me the first 3 times I always swam OUT to the fish to kill them before they hit the village, but after the first wave nothing happened and there was no hidden fish in a rock. The third time, I stayed about in the middle of the village and waited for the enemies to come to me. The main Quaggan guy put up some kind of ice wall and after the first wave the second came. I stayed in the middle of the village for the rest of the encounters and it seemed to work.
Hopefully this helps. Just try staying in the boundaries village and don’t move from there.