The invention relates to a fusible shutter for a hydraulic construction such as a weir, a spillway on a dam or a safety embankment, that comprises a solid member (19) provided on the crest of the construction and maintained thereon by gravity in order to define a watertight or substantially watertight wall, installed on said hydraulic construction and capable of withdrawal so as to let the water flow freely when the level of the reservoir or river reaches a predetermined level, wherein a chamber (2) is formed at the base of the solid member (1) between the latter and the surface bearing same, and pressurising means are used for filling the chamber (2) with water in order to generate under the solid member an upward force when the water of the reservoir or the river reaches the predetermined level. According to the invention, the pressurising means include a water intake level with a supply structure (3) including two compartments (3a, 3b) defined by an inner vertical wall (4), wherein the two compartments (3a, 3b) communicate via at least one passage (5) in the upper portion of the supply structure (3), one of the compartments (3a) having one or more openings in the lower portion thereof for the intake of water from the reservoir or the river into the supply structure (3), while the other compartment (3b) communicates with the chamber (2) under the solid member (1). The invention can be used in a hydraulic construction such as a weir, a spillway on a dam or a safety embankment.