What does a grassy or fishy taste in reservoir water usually indicate?

A grassy or fishy taste in reservoir water often indicates the presence of algae blooms. Algae, particularly certain types like blue-green algae, can produce compounds that give off these distinctive tastes and odors. When conditions are right, such as warm temperatures and high nutrient levels, algae can proliferate extensively, leading to blooms that affect the quality and flavor of the water. This phenomenon is often a natural occurrence but can also be exacerbated by nutrient pollution from sources such as agricultural runoff or wastewater.

Recognizing these tastes in water is essential for water quality monitoring since they can signal the need for treatment adjustments to ensure that the water remains safe and palatable for consumption. The other options do not adequately explain the source of the grassy or fishy taste, as they pertain to different issues in water quality that are not specifically tied to the flavors associated with algal growth.