Both sound and water waves require a
to travel. this means they are

Sound and water waves are mechanical waves; meaning, they require a medium to travel through. The medium may be a solid, a liquid, or a gas, and the speed of the wave depends on the material properties of the medium through which it is traveling.

Explanation:

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."