Help in BiOLogy OL

[Romeo10]

Why when sewage is added to the rivers , Bacteria INCREASE and O2 Decrease and fish decrease ????
Why is this whole thing ?? thx in advance

 

[Zohaib Sherazi]

Acidic water promotes bacterial growth. Bacteria respire using oxygen. Hence, lower oxygen concentration. When oxygen is low fish cannot breath and die. Furthermore sewage adds nutrients which cause growth of the algae. Algae block the entry of sunlight. When there's no sunlight plankton (underwater green plant) makes no food. Hence, fish lose a source of food & die.

 

[Adham-amr]

and that's all called eutrophication