This work reports the implementation and test of a pressure optical sensor suitable to measure, in situ, the sea bed level changes in the nearshore regions. The sensor is based on a fiber Bragg grating (FBG) embedded in a polymeric resin block. The increase of the pressure on the top face of the sensor, due to the change of sediments layer height, results in a change of the FBG Bragg wavelength. The sensor response reveals the capacity to discriminate sea bed level changes down to 2.5 cm, under field survey conditions. Finally, the sensor was successfully tested in a field trial survey at Costa da Caparica, Portugal.