Numerical simulations using a more sophisticated Monte-Carlo technique show that the channel characteristics of an underwater optical wireless communication (UOWC) system are sensitive to angular scattering properties of marine particles (i.e., shape of the phase function), especially in the forward angles (0°-90°). Results of this study include power budget and channel impulse response estimated using different phase functions (Petzold, OTHG, TTHG and SS) and other optical parameters for the cases of harbor waters. Comparison of these results establishes the importance of using an accurate phase function in channel modeling of UOWC systems. Furthermore, comparison with the model based on Beer's law establishes the advantage of considering the finite probability of receiving scattered photons at the receiver end. Our finding reveals that estimation of power loss considering extinction coefficient as in Beer's law severely underestimates the received power, leading to shorter communication range especially in turbid harbor waters. © 2017 IEEE.