(a) Rise in organic matter , leads to increased microbial activity / growth of microbes
(b) It results in decrease in dissolved oxygen / rise in BOD / rise in Biochemical Oxygen Demand
(c) Leads to fish mortality / algal bloom / colour change / foul odour / increase in toxicity
Detailed Answer :
When organic wastes from the urban sewage enter the water bodies, it serves as a food source for microorganisms such as algae and bacteria. As a result, the population of these microorganisms in the water body increases. Here, they utilize most of the dissolved oxygen for their metabolism. This results in increase in the levels of Biodegradable oxygen demand (BOD) in river water and results in the of aquatic organisms. Also, the nutrients in the water lead to the growth of planktonic algae, causing algal bloom. It imparts a distinct colour to the water bodies and deteriorates the water quality resulting in of fishes. Some bloom-forming algae are extremely toxic to human beings and animals.
