Which of the following is NOT listed as a water pollution example?

• A. Sewage
• B. Heat
• C. Oxygen
• D. Pathogens

Answer: (C)

Water pollution concerns substances or conditions that directly degrade water quality. Sewage introduces organic waste and disease-causing organisms, which foul water and disrupt ecosystems. Heat, or thermal pollution, raises water temperatures, which lowers the amount of dissolved oxygen available for aquatic life and stresses organisms adapted to cooler conditions. Pathogens are disease-causing microbes that contaminate water and pose health risks to animals and people. Oxygen itself is a normal, essential component of water; it supports aquatic life and is used as a key measure of water quality. Pollution-related problems occur when oxygen levels are depleted by other pollutants, not when oxygen is present. That’s why oxygen is not listed as a water pollution example.