The error performance of relay-aided underwater wireless optical communication (UWOC) with wavelength diversity is investigated by considering the compound effects of absorption, scattering, and ocean turbulence. The outage probability and average bit error rate (ABER) of the serial-relay UWOC system based on wavelength diversity are derived. The effects of different relay hops, wavelength diversity orders, and anisotropy factors on the system performance of the signal-combining methods are analyzed in detail. It is observed that relay-aided technology can increase the distance of the communication link and effectively alleviate the limitations of underwater wireless optical fading. The results also show that the wavelength diversity system can help to reduce the scintillation effect of ocean turbulence on the received light, thereby reducing the ABER and outage probability of the system. This study is expected to contribute to the development of more robust UWOC systems operating in turbulent oceans.