Underwater optical wireless communication (UOWC) is an emerging technology designed to enable advanced high data rate applications, such as environmental monitoring, underwater exploration, and secure communication for military and defense purposes. Accordingly, a high-capacity UOWC system utilizing dual-polarization states and 16-quadrature amplitude modulation with orthogonal frequency-division multiplexing is proposed. The system leverages a single laser diode operating at 532 nm to generate orthogonally polarized signals that are transmitted along the X and Y polarization axes, achieving an independent data rate of 40 Gbps per polarization state with a total capacity of 80 Gbps. The performance of the proposed system is evaluated through the bit error rate (BER), error vector magnitude (EVM), and constellation diagrams for 10 distinct waterbodies. The findings demonstrate that water types with lower attenuation, such as pure water, Jerlov I, clear ocean, and Jerlov IA, enable longer transmission distances of 13.93, 13, 10, and 10 m, respectively, at a BER below the threshold limit (3.8×10−3) and an EVM of less than 16%. Conversely, higher attenuation in Harbor I and Jerlov III waters leads to shorter achievable ranges of 3 m at the same BER and EVM values.