A horizontal movement of water; currents can be classified as tidal and nontidal; tidal currents are caused by forces of the sun and moon and are manifested in the general rise and fall occurring at regular intervals and accompanied by movement in bodies of water; nontidal currents include the permanent currents in the general circulatory systems of the sea as well as temporary currents arising from weather conditions. For general rules: 1 to 2 kt current is Light, 2 to 3kt current is Mild, 3 to 4kt is Strong and 5kt is Very Strong for the average diver!