This paper presents a distributed model predictive control (DMPC) strategy for an open-channel system based on linearized Saint-Venant equations that are a set of partial differential equations describing the hydraulic dynamics of unsteady flow in open channels or other shallow water with free surface. The system composes of several reaches delimited by underflow gates. By manipulating these gates, the water level in each reach is regulated. Considering the distributed properties of an open-channel system in essence, the distributed control is more applicable than the centralized one. A DMPC algorithm is proposed in which every gate is controlled by a local regulator governing the water levels nearby. Simulation results and analysis for a cascaded multi-reach system are illustrated.