Self-adjusting lumbar support for buoyancy compensator vest

A buoyancy compensator vest, for providing buoyancy at various underwater depths, having a rigid back board, for supporting an air tank vertically on the rear surface of the board at the back of the diver, surrounded in part by a bladder, for inflating and deflating, and a vest back panel including a pair of spaced-apart over-the-shoulder straps projecting from the top panel edge for joining with a pair of side portions extending about the chest of the diver, and a waist belt passing from behind the compensator vest about the panel side portions and the user's waist to complete the vest, the improvement of a pouch, defined by front and rear surfaces and including an openable panel to expose the interior thereof, the pouch interposed the back board and the scuba diver's back and containing a cushion for placement against the back of the diver, to cushion the back board and tank against the diver's spine, the pouch having openings formed therein to allow filling and draining of water during underwater activities, and a flexible strap located in the pouch, pre-bowed outward toward the diver's back and arranged so that the flexible bow is non-collapsible.