Several years ago we had a fish kill here on the OHIO River. The pool of water we are located in (between the locks) moves 20-30 ft depending on the amount of rain upstream in Pennsylvania area.
The kill was said to have been cause because of fertilizer from flooded farm fields, which I suppose did something to the available oxygen in the water.
When the pool subsided . . . . .we had fish hanging in the sapling trees all around the marina, rotting on the shore, and just floating. The sun came out and the rest I will leave to your imagination. . . . . .