If water pollution continues at its present rate, it will eventually

Continued water pollution, especially nutrient enrichment from fertilizers and sewage, triggers eutrophication: excessive algal and aquatic plant growth that shades other plants and later dies off. The subsequent microbial decomposition of that biomass consumes large amounts of dissolved oxygen, causing hypoxic or anoxic conditions in the water. As dissolved oxygen falls, oxygen becomes unavailable to many aquatic organisms and plants, leading to ecosystem collapse and mass die-offs [2]. Texts specifically note that nutrient loading leads to algal blooms, decomposition further depletes oxygen, and polluted waters have reduced dissolved oxygen levels that eliminate sensitive plankton, fish and other biota [3]. Therefore option 3 is correct.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > 4.3. EUTROPHICATION > p. 36
2. [2] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > Water Pollution > p. 33
3. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > r. Effect$ oa aquatic eco$ystem: > p. 75