Concept:Water pollution is the contamination of water bodies by harmful substances.
Sand filling is a land modification process, not a direct cause of water pollution.
Explanation:Increased silt load from erosion makes rivers and lakes muddy, reducing water quality.
Sewage deposit adds human waste, organic matter, and disease-causing organisms into water.
Industrial effluent releases chemicals, toxins, and heated water into rivers and seas.
Sand filling, however, involves depositing sand on land, often to reclaim or raise ground level.
It does not directly contaminate water bodies.
Answer:C. sand filling.