Untethered liquid crystal elastomer (LCE) fiber actuators are promising candidates for soft actuators due to their analogies to biological muscles. However, most LCE fiber actuators are difficult to (re)program and primarily only work in air, which significantly hinders their underwater applications. Here, tens-of-meters-long, millimeter-diameter, light-responsive, amphibious LCE fiber actuators with high actuation force are fabricated by melt extruding a thermoplastic LCE containing azobenzene photoswitches and hydrogen-bonding crosslinks. The dynamic hydrogen bonds enable the fibers to be reprogrammed into stretched, twisted, or coiled configurations. The actuators demonstrate contracting/expanding and simultaneous rotating motions under ultraviolet light both in air and water environments. The twisted and helical fiber actuators demonstrate rotations of 57° mm−1 and 14° mm−1, respectively, while lifting loads up to 0.08 g underwater, which is approximately 28 times greater than their own weight. The actuation performance enables the control of the movement of an embedded optical fiber while emitting light and the opening and closing of a fiber-sewn fabric in water. A woven multi-material textile sequentially demonstrates contraction in the longitudinal direction under light stimulus in water, followed by contraction in the latitudinal direction under heat stimulus. This work provides a strategy for fabricating light-responsive underwater fiber actuators, with potential applications as artificial muscles and biomedical devices.