A floating covering (4) on the liquid content of a storage tank (1) with vertical side wall, wherein the circumferential edge (18) of the covering (17) is provided with an annular closing body (6) of elastic material lying against the tank side wall, provided with a hollow gas-tight annular space (20), which can be connected up to a pressure source (12). By relieving pressure in the annular space the closing body (6) can retract slightly as a result of which friction is reduced; as soon as the required liquid level is reached the hollow body can be connected onto the pressure source (20) so that the closing body in "inflated" up against the side wall.
