Current wave

Whitewater waves are produced by the energy of the water current interacting with bottom obstructions. These waves usually manifest themselves as haystacks or standing waves. When current is force through a restriction between two rocks or over the top of a ledge it must accelerate. After the restriction the water slows down again when it has more space to move. However, it still contains a lot of kinetic energy which must be disipated. This energy is manifested in the form of waves.

On the ocean current waves are not common, however strong tidal currents can create rips where the current is squeezed through a restriction.