Studies conducted over the last ten years have resulted in the construction of a lock and barrage on the Sarawak River in the state of Sarawak, Malaysia. The barrage controls river and tidal flows and has eliminated most of the tidal variation in water level which was formerly experienced in Kuching, the state capital of Sarawak. This paper reviews the hydrotechnical and geotechnical studies of the river and outlines the current operation and effects of the barrage.