How does excessive nutrient runoff impact water ecosystems?

Excessive nutrient runoff significantly impacts water ecosystems by leading to harmful algal blooms. When nutrients, particularly nitrogen and phosphorus, enter water bodies in excess, they can promote rapid growth of algae. This phenomenon, known as algal blooms, can deplete oxygen levels in the water as the algae die and decompose, creating hypoxic conditions that can be detrimental to aquatic life. Additionally, some algae produce toxins that are harmful to fish, wildlife, and even humans. This disruption not only affects the biological balance of aquatic ecosystems but also impacts water quality and recreational activities. The health of the entire aquatic ecosystem can be compromised due to these blooms, illustrating the serious consequences of nutrient pollution from runoff.

In contrast, options like increasing water clarity, reducing aquatic plant growth, and stimulating fish population growth do not accurately reflect the outcomes of nutrient runoff; rather, they overlook the environmental challenges that arise from these excess nutrients.