How do excessive nutrients in water contribute to algal blooms?

Excessive nutrients in water, particularly nitrogen and phosphorus, serve as fertilizers for aquatic plants and algae. When nutrient levels rise significantly, they encourage rapid and often uncontrolled growth of algae, leading to algal blooms. These blooms can cover the surface of the water, blocking sunlight and disrupting the ecosystem. The dense growth depletes oxygen levels when the algae die and decompose, which can lead to hypoxic conditions that harm aquatic life.

The other options do not relate directly to the role of excessive nutrients in algal bloom development. Slowing down photosynthesis or increasing water filtration don't accurately describe the effects of high nutrient levels. Similarly, fish migration is generally a response to changes in habitat quality rather than a direct result of nutrient excess. Thus, the statement that excessive nutrients promote rapid algal growth captures the essential biological mechanism behind algal blooms.