Which of the following is a primary cause of algal blooms in waterways?

Nutrient pollution is indeed a primary cause of algal blooms in waterways. This phenomenon occurs when excessive nutrient inputs—particularly nitrogen and phosphorus—enter water bodies, often as a result of runoff from agricultural activities, sewage discharge, or industrial waste. These nutrients serve as fertilizers for algae, leading to rapid and uncontrolled algal growth.

When conditions are right, such as warm temperatures and ample sunlight, the excess nutrients can trigger significant algal blooms, which can have detrimental effects on aquatic ecosystems. The blooms can deplete oxygen levels in the water when the algae die and decompose, leading to hypoxic conditions that adversely affect fish and other aquatic life. In some cases, certain algal blooms can produce toxins that are harmful to both aquatic organisms and human health.

In contrast, factors such as high levels of dissolved oxygen, low water temperature, and increased biodiversity do not contribute to the proliferation of algal blooms and, in certain contexts, may even help to mitigate their impacts.