Question

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

Answer 1

Excessive phytoplankton (organic pollutants such as leaves, grass, trash, etc.) present in water is biodegradable. large population of bacteria decomposes this organic matter in water. During this process, they consume the oxygen dissolved in water. Water has already limited dissolved oxygen (10 ppm). Thus, it is further depleted When the level of dissolved oxygen falls below 6 ppm the fish cannot survive Hence, they die and lot dead on the lake