Which of the following is a water quality indicator?

• A. Turbidity
• B. Temperature
• C. pH
• D. Salinity

Answer: (A)

Water quality indicators are measures that reveal how healthy a body of water is for organisms and human use. Turbidity fits this idea well because it directly shows how much stuff is suspended in the water. When soil erodes or runoff carries sediment into streams, turbidity goes up. Those particles cloud the water, block sunlight needed by aquatic plants, and can clog fish gills or smother bottom habitats. Suspended solids often carry nutrients and contaminants as well, so a spike in turbidity can signal broader water quality problems. It’s also convenient to measure in the field with a Secchi disk or a turbidity meter, and it responds quickly to rainfall and land-use changes, making it a practical and widely used indicator.

Temperature, pH, and salinity are certainly important characteristics of water, but they’re not as direct a sign of pollution entering a water body as turbidity. Temperature affects dissolved oxygen and ecosystem processes, pH shows acidity/alkalinity, and salinity indicates salt content—especially relevant in estuaries and coastal areas. They describe conditions, but turbidity specifically signals sediment and runoff-related water quality issues.