Bats use SONAR (Sound Navigation & Ranging).Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.
Plunge pool or waterfall lake is a deep depression in the stream bed at the base of the waterfall. It is created by the erosional force of the cascading water. They occur at the youthful stage of the river development.