Northward- or southward-directed ocean-water current which flows parallel and close to a continental margin. Such currents are caused by the deflection of eastward- and westward-flowing currents by the continental land masses. Boundary currents on the western margins of ocean basins, such as the Gulf Stream and the Kuroshio current, are deep, narrow, fast-moving currents carrying warm water; while currents along the eastern boundaries, such as the Canaries current and the California current, tend to be relatively shallow, broad, diffuse, slow-moving, and carry cool water.