What is the primary effect of excessive algae growth in a water system?

The primary effect of excessive algae growth in a water system negatively affects dissolved oxygen levels. When algae proliferate, especially in conditions of high nutrient availability, they can lead to a process called eutrophication. This occurs when algae consume the available nutrients and grow rapidly. During the day, algae produce oxygen through photosynthesis; however, at night, or when they die off, they undergo decomposition which requires oxygen. This decomposition can reduce the dissolved oxygen levels in the water, leading to hypoxia or anoxic conditions, which are harmful to aquatic life.

In contrast, options such as enhancing water clarity or reducing water temperature do not align with the realities of excessive algae growth. Algae blooms often create a murky, less transparent water body, thereby decreasing clarity. Furthermore, by absorbing sunlight and blocking it from reaching other aquatic plants, they can also disrupt the natural water temperature regulation, although they do not actively reduce the temperature themselves. Additionally, while nutrient levels may initially increase due to algae, the main concern is not the nutrient levels themselves but rather the biological impact on oxygen availability in the ecosystem.