What is a common consequence of agricultural runoff affecting water sources?

Agricultural runoff often contains fertilizers, pesticides, and other chemicals that can significantly impact nearby water sources. One major consequence of this runoff is the increase in nutrient levels, particularly nitrogen and phosphorus, in the water. These nutrients promote the rapid growth of algae, leading to algae blooms. These blooms can diminish water quality, reduce sunlight penetration, and disrupt ecosystems by consuming available oxygen when they decompose. As a result, freshwater bodies can experience oxygen depletion, negatively affecting aquatic life.

The other options do not accurately represent the direct effects of agricultural runoff. Elevated pH levels and lower water temperatures are not typical outcomes related to nutrient-driven runoff, while reduced visibility may occur as a secondary effect of algae blooms or other pollutants but does not capture the primary consequence associated with nutrient loading. Thus, the increase in algae blooms stands out as the most direct consequence of agricultural runoff.