Underwater optical wireless communication (UOWC) systems are attracting attention in the context of beyond 5G/6G networks for their capacity to ensure reliable and high-data-rate communications. The system under consideration consists of underwater nodes communicating with an onshore base station through relay nodes. In such scenarios, system performance can be affected by pointing errors resulting from the movements of both underwater and relay nodes. In this paper, we investigate the end-to-end performance of a UOWC-free space optical (FSO) system under the influence of pointing errors while considering the depth-dependent characteristics of the underwater link. We present a comprehensive mathematical model that accounts for relevant impairments, including attenuation, turbulence, and pointing errors. A closed-form expression for the outage probability is derived by applying the cascaded underwater turbulence model. The results obtained highlight the validity of using a cascaded turbulence model. We also show that it is possible to determine an optimal system configuration, specifically the beam radius at the receiver, to alleviate the induced fading caused by pointing errors, thereby enhancing the end-to-end system performance.