The sluice oscillates about a shaft (16) in order to control the level of a downstream reach (4) to occupy a reference level as defined by the position of an opening (36) for connection to the atmosphere and suitable for being closed by a needle (38) carried on a float (40). The plate (6) is driven by a caisson (18) which is immersed in the upstream reach (2) and which contains a quantity of water (28) that is increased by sucking air via a hydraulic Venturi (50) driven by the flow of water between the two reaches. The displacements of the float (40) control the pressure reduction which is actually applied to said caisson in such a manner as to obtain the desired level control. The invention is applicable to controlling irrigation networks.