A water power turbine energy conversion device and method of generating electric power that can take advantage of water current speeds is hereinafter disclosed. The water power turbine energy conversion device includes an unmanned tethered aquatic device (TAD) connected to one end of a tether (which may include multiple shorter tethers), the other end being connected to an anchorage point. The TAD comprises a hydrofoil wing-like structure with one or more water power turbines and performs waterborne maneuvers such as cross-current tracking to increase the relative water current speed of up to about four times the true water current speed.