What condition is caused by nutrient overloading and decay of algae, leading to low levels of oxygen in water?

The condition described is primarily tied to the process of hypoxia, which specifically refers to low levels of dissolved oxygen in water bodies. This situation often arises as a result of eutrophication, where the overloading of nutrients, particularly nitrogen and phosphorus, leads to excessive algae growth. When these algae die, they decompose, a process that consumes a significant amount of oxygen in the water, leading to hypoxia.

While low dissolved oxygen is a direct consequence of this process, hypoxia is the term that specifically defines the insufficient oxygen levels that can affect aquatic life. Therefore, the correct answer points to hypoxia as it encapsulates the effects of nutrient overload and algal decay on oxygen levels in aquatic environments.

The confusion may arise from the close relationship between these concepts. Acidification refers to a lowering of pH levels in water, which is not directly related to the oxygen depletion caused by algal blooms and nutrient overload.