The misalignment of mobile underwater wireless optical communication (UWOC) systems, compounded by misalignment in underwater mobility scenarios, is a practical problem that can be resolved through various means. This work describes a pulse-position modulation (PPM) based diffused-line-of-sight UWOC system that offers a solution to this issue. PPM is found to be power-efficient and, in terms of bit error ratio performances, outperforms on-off keying modulation and orthogonal frequency-division multiplexing modulation in complex dynamic underwater channels. Through indoor experiments and an outdoor deployment, herein, we validated the robustness of our PPM-based mobile UWOC system. This work is expected to shed light on practical implementation of UWOC network for relieving the strict positioning-acquisition-and-tracking requirements when underwater apparatus is transmitting or receiving signals on-the-fly.