Scientists today are studying tidal power as an alternative energy source for generating electricity. Some scientists conclude that tidal power is a good alternative source of energy because it uses a natural process, does not rely on fossil fuels, and does not release greenhouse gases. These scientists recommend building tidal power plants around the United States in locations with high tidal power potential. Other scientists conclude that tidal power is not a good alternative energy source because tidal power plants can negatively impact the surrounding ecosystem by killing marine animals, restricting fish migration, reducing the natural flow of water, and causing silt buildup in waterways. These scientists recommend not building tidal power plants in U. S. waterways. Both conclusions are based on valid data and scientific reasoning. How can both conclusions be valid?