How can sewage discharge affect the aquatic creature ?

How does the unrestricted growth of weeds in water bodies affect the aquatic animals ?

A large quantity of urban sewage is drained to a nearby river. Which among the given conditions would happen after mixing of sewage into the river (i) BOD of receiving water body increases (ii) DO of receiving water body decreases (iii) It will not cause mortality among fishes and other aquatic creatures. (iv) It will lead to nutrient enrichment of receiving water body

A large quantity of urban sewage is drained to a nearby river. Which among the given conditions would happen after mixing of sewage into the river (i) BOD of receiving water body increases (ii) DO of receiving water body decreases (iii) It will not cause mortality among fishes and other aquatic creatures (iv) it will lead to nutrients enrichment of receiving water body

Explain how does the inflow of large amount of nutrients like phosphates and nitrates into the water body drastically affects the aquatic life there. Name the phenomenon responsible.

How can waterlogging affect the growth of crop ?

Explain the change that can be observed in the characterstics of river water when sewage is discharged into it and a few weeks after the discharge with respect to (i) level of dissolved oxygen (ii) Population of fresh water organisms.