Previous studies on the hydrological excitation of the Earth's polar motion have neglected the effect of water mass variations of hydrological reservoirs that have time scales much longer than a month. To remedy this, the present paper calculates the polar motion excitation caused by variations in major natural lakes, the impoundment in artificial reservoirs, and the depletion of a major groundwater aquifer. It is found that (1) the annual water mass variation in natural lakes contributes a significant fraction in the total hydrological excitation of the annual wobble, (2) the hydrological reservoirs have been negligible in the Chandler wobble excitation, and (3) the contribution of hydrological reservoirs to the total secular polar drift has been negligible in this century due to fortuitous cancellation among reservoirs.