How phosphorous nitrogen and calcium increase the bod of water although they are required by aquatic plants?

Phosphorus, nitrogen, and calcium are essential nutrients for aquatic plants, promoting their growth. However, when present in excess due to runoff from agriculture or urban areas, they can lead to eutrophication, a process where nutrient overload stimulates rapid algal blooms. These blooms can deplete oxygen in the water, harming aquatic life and degrading water quality. Thus, while these nutrients are necessary for plant health, their overabundance can significantly disrupt aquatic ecosystems.