Which two factors are commonly used to assess river water quality?

• A. Temperature and color
• B. pH and salinity
• C. Nitrate levels and turbidity
• D. Density of fish

Answer: (C)

Water quality is assessed by looking at measurements that show nutrient levels and how clear the water is. Nitrate levels indicate nutrient pollution from fertilizer runoff or wastewater, and when nitrates are high, algae can grow too much. When algae die, they decompose and use up oxygen, which can harm fish and other aquatic life. Turbidity measures how murky the water is due to suspended sediments or organic matter; high turbidity lowers light in the water, can clog gills, and signals erosion or pollution.

Other options don’t align as directly with standard water-quality checks. Temperature and color can reveal conditions, but they don’t give a consistent measure of pollution or ecosystem stress the way nutrients and clarity do. Density of fish reflects overall ecosystem health, but it’s a biological outcome influenced by many factors beyond water chemistry and isn’t a direct water-quality parameter.