This letter presents the design and implementation of an underwater simultaneous lightwave information and power transfer (U-SLIPT) prototype system. The system features a U-SLIPT receiver that combines a multicrystalline silicon (Si) solar panel with an avalanche photodiode (PD) to simultaneously enhance both energy harvesting (EH) and information decoding (ID) performances. Subsequently, we evaluate the EH and ID capabilities of the proposed U-SLIPT prototype system through extensive empirical experiments. Based on the experimental and simulation results, we propose two operational strategies to optimize the system’s performance according to its intended purpose. The first strategy involves determining the optimal transmitter-receiver distance to maximize EH and ID without considering unexpected movements. The second strategy focuses on selecting the appropriate reference voltage for the PD, which is crucial for accurately distinguishing digital signals. These strategies are essential for the effective operation of U-SLIPT systems in dynamic underwater environments.