How does agricultural runoff typically affect surface water quality?

Agricultural runoff significantly affects surface water quality by introducing nutrients and pollutants, particularly nitrogen and phosphorus, into water bodies. When these nutrients accumulate, they can lead to eutrophication, a process characterized by excessive growth of algae in the water. This overgrowth can deplete oxygen levels, creating dead zones where aquatic life struggles to survive. Additionally, as algae die off and decompose, this further compounds the oxygen depletion issue, ultimately harming fish and other species dependent on stable, healthy aquatic environments.

This phenomenon illustrates the importance of monitoring and managing agricultural practices to minimize runoff and protect water quality in surrounding ecosystems. The other options do not accurately represent the impact of agricultural runoff; rather, they underestimate or mischaracterize the severity of its effects.