In this paper, we propose a statistical channel model to study the performance of a line-of-sight underwater wireless optical communication (UWOC) link in a data mulling environment. We optimize the range of geometric parameters including detector aperture diameter and field-of-view (FOV) to reduce the effect of excessive scattering on the optical signal. By considering geometric losses, we observe how many photons are absorbed and deviated from the optical axis causing temporal dispersion and fading of the optical signal. Furthermore, we apply photon counting method to evaluate the system in terms of bit error rate (BER). Our simulation results show that scattering is one of the important degrading effects among absorption, pointing loss, and channel loss caused by underwater channel on propagating optical signals. Moreover, the results suggest that a change in the aperture of the photon collector improves the BER performance.