Which of the following can be an indicator of water pollution in agricultural settings?

Excessive algae growth and fish kills serve as significant indicators of water pollution in agricultural settings for several reasons. When agricultural runoff occurs, often rich in nutrients such as nitrogen and phosphorus from fertilizers, it can lead to nutrient over-enrichment in water bodies. This condition promotes algal blooms, which is the rapid increase of algae in water. These blooms can result in a thick layer of algae on the surface, blocking sunlight and disrupting the aquatic ecosystem.

When the algae die and decompose, the decomposition process consumes oxygen in the water, leading to hypoxic (low oxygen) conditions. This can be detrimental to aquatic life, particularly fish, which depend on dissolved oxygen to survive. As a result, fish populations can decline sharply, often leading to fish kills, where large numbers of fish die in a water body due to oxygen deprivation.

Consequently, the presence of excessive algae growth coupled with the occurrence of fish kills highlights a disrupted ecosystem and points to potential water quality issues stemming from pollution sources, making it a reliable indicator of water pollution in agriculture.