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a type of turbulence at sea in which wave motions and eddy currents are combined on the surface. The movement of water particles in overfalls is similar to the motion of such particles on the surface of boiling water. Overfalls result from a sharp change in the velocity of a current, particularly, a tidal current, when the current emerges from a narrow place or from behind a cape; they also may arise when two streams meet. The waves associated with overfalls are high amd may reach 4 m in some regions, for example, in the Arctic Ocean near bays or inlets fed by large rivers; such waves are dangerous for small craft.