Water Pollution

The Yamuna river in Delhi faces serious pollution primarily due to the dumping of domestic sewage and waste. A significant portion of untreated domestic wastewater is discharged into the river, causing high levels of organic pollution and water quality deterioration.
Flood water spreading (A): Contributes little to pollution compared to direct waste dumping.
Dumping of domestic waste (B): Major cause of pollution, leading to depletion of dissolved oxygen and harming aquatic life.
Use of pesticides (C) and fertilizers (D): These affect water bodies mainly through agricultural runoff, less relevant in Delhi's urban pollution. So, the correct answer is (B): Dumping of domestic waste.

The primary source of pollution in the Yamuna River in Delhi is the dumping of domestic waste. Due to rapid urbanization, untreated sewage, household waste, and industrial effluents are directly released into the river. This has led to severe water pollution, with high levels of toxins and waste in the water. While the use of pesticides and fertilizers does contribute to pollution in agricultural areas, the dumping of domestic waste is the most significant factor in polluting the Yamuna in Delhi. Thus, the correct option is (B) Dumping of domestic waste.