A river with an inflow of domestic sewage rich in organic waste may result in Drying of the river very soon due to algal bloom, An increased production of fish due to biodegradable nutrients, Death of fish due to lack of oxygen, Increased population of aquatic food web organisms

Eutrophication is the natural aging of a lake by nutrient enrichment of its water. With time, streams draining into the lake introduce nutrients such as nitrogen and phosphorus and domestic sewage, which encourage the growth of aquatic organisms. As the lakes fertility increases, algal bloom occurs. Algal bloom causes the degradation of water quality and fish mortality and dead remains begin to be deposited on the lake bottom. Over the years, the lake finally converts into land. Thus, the correct answer is option C (Death of fish due to lack of oxygen). The excessive growth of algae depletes the dissolved oxygen in the water, leading to the death of fish.