Sewage containing organic waste should not be disposed in water bodies because it causes major water pollution. Fishes in such a polluted water die because of

• A

  large number of mosquitoes
• B

  increase in the amount of dissolved oxygen
• Correct answer
  C

  decrease in the amount of dissolved oxygen in water
• D

  clogging of gills by mud

Hence, the correct answer is option: 'C'.