 The water level of the Caspian Sea has varied within 4 m over a period of 30 years.Water levels in the Caspian Sea down to true altitude of -29 m reduce the depth of the lower Volga and restrict ship movement in this part of the Volga-Don Waterway.A shipping lock in the Manych Ship Canal near the Caspian Sea could be designed to control this water level fluctuation.