Apparatus and method is disclosed for generating usable power derived from oscillatory hydro-kinetic energy available in the movement of waves having a given height and being spaced apart by a predetermined distance at the surface of a body of water. Apparatus and method is disclosed for generating usable power derived from hydro-kinetic energy available in a body of water moving in at least one direction of movement, the at least one direction being substantially horizontal or substantially vertical. Apparatus and method is disclosed for generating usable power derived from hydro-gravitational forces available at a site having a source of water at a first elevation higher than a second elevation at a selected location where the usable power is to be derived.