How does algae typically appear in water?

Algae in water often appear as microscopic organisms that can create noticeable changes in the water's color, often giving it a green or yellow-green hue. This phenomenon is due to the presence of chlorophyll within the algae, which allows them to photosynthesize and thrive in nutrient-rich environments. When conditions are favorable, such as excess nutrients or warm temperatures, these microscopic algae can multiply rapidly, leading to what is referred to as algal blooms. These blooms may not always be seen as large surface formations, but they can significantly impact the clarity and quality of the water, contributing to issues such as reduced oxygen levels and aesthetic problems.

While large visible blooms (the first option) do occur, they are more commonly associated with surface algae and are usually a result of more extensive growth, not the primary way algae typically starts to affect water quality. Algae do not usually exist as a clear layer at the bottom of bodies of water (the third option), which is more characteristic of sediment or debris accumulation. Floating debris (the fourth option) can result from various sources, but it is not specifically indicative of algae presence. Therefore, the microscopic algae that color the water are the most representative form of algae in typical aquatic environments.