What does an algae bloom look like?

An algae bloom is characterized by the substantial growth of algae in a body of water, which can lead to visible color changes and patterns on the surface. The correct answer indicates that blooms can cause colors such as red, black, or oily streaks, presenting a noticeable and often striking appearance. This phenomenon typically results from an increase in nutrient levels—especially nitrogen and phosphorus—combined with suitable environmental conditions such as warmth and sunlight. The visible discoloration can vary depending on the types of algae present, and it’s often associated with a range of ecological issues, including oxygen depletion and toxins in the water.

In contrast, dispersed algae without significant color change would not represent a bloom, as blooms are defined by their density and visible coloring. Large clusters sinking to the bottom would not generally be classified as an algae bloom since blooms are seen mainly at or near the water surface. Lastly, the mention of a seasonal appearance only during winter would not accurately reflect the conditions under which algae blooms can occur, as these can happen in various seasons based on environmental factors. Thus, the identification of blooms by their colorful and often dramatic surface presence aligns with the characteristics that define them in aquatic ecosystems.