This invention relates to a submerged buoy (1) consisting of: a housing (2) containing a receiver (4) of a radioacoustic signal; a mooring rope (11) with one end attached to a mooring point; a mechanism for releasing said buoy, allowing it to return to the surface; and a flotation reserve; said buoy being noteworthy in that the release mechanism (7) is of electromechanical type and is enclosed in a hermetically sealed tank (5) which thus forms the flotation reserve; said mechanism (7) controlling a catch (8) which either prevents or allows the free rotation of a winding drum (10) around which the mooring rope (11) is wound. This buoy may be used particularly for marking submerged objects such as fishing equipment, nets, fish pots etc., for controlling mooring sites in pleasure ports or even to mark off a sensitive area (such as around an underwater mine).