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.

A lake near a village suffered heavy mortality of fishes within a few days. Consider the following reason for this i) Lots of urea and phosphate fertilzers were used in the crops in the vicnity. II)The area was sprayed with DDT by an aircraft . The lake water turned green and stinky. Phytoplankton population in the lake decilend initially therby greatly reducing photosynthesis. which two of the above were the main causes of fish mortality in the lake?