How does agricultural runoff contribute to water quality issues?

Agricultural runoff plays a significant role in contributing to water quality issues primarily through the introduction of pesticides and fertilizers into water bodies. When it rains, water flows over agricultural fields and can carry with it a variety of contaminants. Pesticides, which are used to control pests, can seep into nearby streams, rivers, and lakes, affecting aquatic life and potentially entering drinking water supplies. Fertilizers, especially those rich in nitrogen and phosphorus, can also wash off fields and enter water bodies, leading to nutrient pollution.

This influx of nutrients can trigger algal blooms, which deplete the oxygen in the water as they decompose, creating dead zones where aquatic life cannot survive. Additionally, these harmful substances can disrupt aquatic ecosystems and pose risks to human health as they may accumulate in fish and shellfish. Hence, the introduction of such chemicals through runoff is a primary concern in water quality management.