Biofouling mitigation measures for optical ports can extend the duration of oceanographic deployments, but there have been few quantitative studies of field performance. Results are presented from a 4-month field test of a stereo-optical camera system intended for long-term environmental monitoring of tidal turbines. A combination of passive (copper rings and ClearSignal antifouling coating) and active (mechanical wipers) biofouling mitigation measures are implemented on the optical ports of the two cameras and four strobe illuminators. Biofouling on the optical ports is monitored qualitatively by periodic diver inspections and quantitatively by metrics describing the quality of the images captured by cameras with different antifouling treatments. During deployment, barnacles colonized almost every surface of the camera system, except the optical ports with fouling mitigation measures. The effectiveness of the biofouling mitigation measures suggests that 4-month deployment durations are possible, even during conditions that would otherwise lead to severe fouling and occlusion of optical ports.