A multimode fiber-optic hydrophone based upon a Schlieren intensity modulation mechanism is described. The device possesses sufficient sensitivity to detect the Knudson sea noise levels in the frequency range 100 Hz to 1 kHz and to detect static displacements as small as 2.5 × 1013 Å. It is not susceptible to phase noise and is relatively insensitive to static pressure head variations. The hydrophone is electrically passive. Ease of fabrication, potential low cost, and compatibility with present multimode fiber-optic technology make this device an attractive candidate for incorporation into practical fiber-optic acoustic sensing arrays.