Which energy source is generally free of air pollution or solid waste during operation, yet construction can alter aquatic habitats?

• A. Nuclear power
• B. Coal-fired power
• C. Natural gas
• D. Hydroelectric power

Answer: (D)

Hydroelectric power stands out because it uses falling water to spin turbines, so there are no fuel combustion emissions or solid waste produced during operation. That means air pollution and solid waste are generally absent while it’s generating electricity. The trade-off comes from construction: building a dam and creating a reservoir can dramatically alter aquatic habitats by changing water flow, sediment transport, and temperature, disrupting fish migrations and other ecosystem processes. In contrast, nuclear power does produce solid waste (spent fuel) and can have long-term waste concerns, coal-fired power emits air pollutants and produces solid waste, and natural gas, while cleaner, still releases some pollutants during operation. So the best fit is hydroelectric power.