What is a likely effect of nutrient runoff into waterways?

Nutrient runoff into waterways, often from agricultural fertilizers or urban runoff, leads to increased levels of nutrients, particularly nitrogen and phosphorus, in the water. This excessive nutrient load triggers algal blooms, which can dramatically diminish water clarity as the dense populations of algae proliferate. These blooms can block sunlight from reaching aquatic plants, which ultimately disrupts the aquatic ecosystem's balance. As algae die and decompose, oxygen levels in the water can also drop, leading to further negative impacts on aquatic life.

In contrast, improved aquatic biodiversity, increased fishing yields, and reduction in algal blooms would unlikely occur as a result of nutrient runoff. Instead, the adverse effects, primarily manifested in diminished water clarity due to algal proliferation, clearly highlight the environmental challenges posed by nutrient pollution in aquatic systems.