How does fertilizer affect a pond?

Fertilizer can significantly impact a pond by introducing excess nutrients, primarily nitrogen and phosphorus, which can lead to algal blooms. These blooms can deplete oxygen levels in the water, harming aquatic life and disrupting the ecosystem. Additionally, when algae die and decompose, the process further reduces oxygen levels, potentially leading to fish kills and decreased biodiversity. Overall, the overuse of fertilizers can result in water quality deterioration and disrupt the balance of the pond's ecosystem.