Explain the effect on the characteristics of a river when (3 marks)
urban sewage is discharged into it.
- Rise in organic matter , leads to increased microbial
activity / growth of microbes= ½ + ½
-It results in decrease in dissolved oxygen / rise in BOD /
rise in Biochemical Oxygen Demand = 1
- Leads to fish mortality / algal bloom / colour change / foul odour /
increase in toxicity (Any two) = ½ + ½ (1+1+1 marks)