<p>Caisson quay walls with calcareous sand backfill (CQW-CSB), as the main form of gravity marine structures, are prone to large deformation or even instability during earthquakes. Fiber reinforcement is an effective measure to greatly enhance the seismic performance of CQW-CSBs. However, its seismic behavior under conditions of large water level fluctuations caused by dynamic hydrology such as tidal effects and extreme precipitation has not been systematically studied. In this study, a series of shaking table tests were carried out to investigate the influence of water level changes on the seismic performance of caisson quay wall with fiber-reinforced calcareous sand backfill (CQW-FRCSB). The test results show that the acceleration amplification factor, horizontal dynamic soil pressure, and excess pore water pressure gradually increase with increasing water level, indicating that high water level has an adverse effect on the seismic stability of CQW-FRCSBs. In addition, regardless of the water level, fiber reinforcement can effectively limit the excess pore water pressure below the liquefaction threshold even under strong seismic excitation, thereby preventing large deformations caused by liquefaction. Moreover, increasing the water level exacerbates the horizontal displacement, ground settlement, and surface cracks propagation of quay walls. At an input acceleration of 0.6&#xa0;g, a rise in water level induces significant horizontal displacement and settlement that is at least 476% and 280% greater than that of a structure backfilled with dry soil. Overall, the seismic design of CQW-CSB should carefully consider water level changes, and fiber reinforcement is an effective technology to improve its seismic performance.</p>