Sewage containing organic waste should not be disposed of in water bodies
because it causes major water pollution. Fishes in such polluted water die
(i) Large number of mosquitoes.
(ii) Increase in the amount of dissolved oxygen.
(iii) The decrease in the amount of dissolved oxygen in the water.
(iv) Clogging of gills by mud.
Option (iii) The decrease in the amount of dissolved oxygen in the water is the answer.