Abstract: The flood barrier includes a chamber with a first side wall and a second side wall, a water inlet for letting in water, a single support block arranged on the first side wall, and a dam wall up and down movably arranged in the chamber. The dam wall forms a retaining wall for restraining water flow, a forcing element for causing an upward movement of the dam wall, and a blocking element for providing a blockade for limiting the upward movement, the blocking element. The support block has an inclined surface against which the inclined surface of the blocking element acts in a closed state of the flood barrier. Due to the orientation of the angled wall of the support block, the blocking element is forced to move sideward and thereby a lateral force is created forcing the dam wall to one side of the chamber.