Along with lowering DO levels, what other effect does organic pollution have on aquatic life?

Organic pollution significantly impacts aquatic ecosystems, particularly through the encouragement of algae growth. When organic matter, such as sewage, enters the water, it provides a rich source of nutrients—especially nitrogen and phosphorus—that stimulate the proliferation of algae. This phenomenon is known as eutrophication.

As algae bloom and multiply due to the abundance of nutrients, several changes occur in the aquatic environment. For one, dense algal blooms can block sunlight from reaching submerged aquatic plants, disrupting photosynthesis and negatively affecting those organisms. Moreover, as algae die and decompose, the process consumes oxygen in the water, leading to decreased dissolved oxygen levels, which can be detrimental to fish and other aquatic life.

The other options do not accurately characterize the effects of organic pollution. Organic pollution typically leads to an increase in nutrients rather than a decrease, so the first choice is not applicable. While increased water temperature can occur due to various environmental factors, it is not a direct effect of organic pollution itself. Improved recreational activities are unlikely due to the negative impacts of organic pollution on water quality and aquatic life. Overall, the encouragement of algae growth is a central and direct consequence of organic pollution in aquatic environments.