A water-gate is intended to withstand pressure exerted by a liquid. The water-gate includes an essentially flat shell plate and a plurality of thin cores extending along the length of the shell plate, the thin cores being substantially parallel to one another. Each core is solidly connected to the shell plate and pierced with multiple disjoint holes. According to the disclosure, the water-gate comprises at least one stiffener formed by assembling multiple elements that are aligned along a longitudinal axis of the stiffener and that each extend between the cores without passing through the cores. Each element may be solidly connected to a face of at least one core around one of the holes.