A waterfowl decoy motion system comprises a self-propelled floating decoy tethered to a submerged line supported below the surface of a body of water by stakes driven into the water bottom. A thruster is attached to the bottom of the decoy such that the direction of propulsion is offset from a longitudinal axis extending along the length of the decoy by an angle of at least one degree. The tether is slidably attached to the submerged line, and a swivel located on the tether allows the decoy to rotate freely. The decoy is guided by the line as it moves across the surface of the water. When the tether reaches a stopper near each end of the line, the offset propulsion angle causes the decoy to turn in an arcing path, turn around, and travel in the opposite direction. The decoy repeats this process in a continuous loop.