Which best determines the health of a lake used as a source of freshwater?

• A. its depth and width
• B. its temperature and pH
• C. its location and depth
• D. its temperature and depth

Answer: (B)

Temperature and pH most directly relate to water quality, making them the best indicators of a lake’s health for freshwater use. Temperature influences how much dissolved oxygen the water can hold—warmer water can hold less oxygen, which affects fish and other aquatic life and can impact treatment processes. pH shows how acidic or basic the water is, which changes the solubility and toxicity of chemicals and nutrients and affects which organisms can thrive. Together, these two factors capture the chemical and biological conditions that determine whether the lake is healthy enough to supply safe drinking water.

Physical size or location—while important for other reasons—does not by itself reveal current water quality. Depth alone doesn’t tell you about contaminants or oxygen levels, and width or location don’t directly indicate how suitable the water is for use.