A large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping but you find an abundance of phytoplankton. Suggest a reason for the fish kill.

Question

Philoid · Accepted Answer

The reasons may vary. One case can be the BOD level change of the lake water. The abundance of phytoplankton can cause the decrease in oxygen level of water because phytoplankton is degraded by bacteria with the help of dissolved oxygen. Since oxygen demand increases, its harder for the fishes to survive on that condition which may cause their death.