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The southern Benguela Current region off South Africa is subject to frequent harmful algal blooms (HABs), which can have serious impacts — both through the introduction of toxins into the ecosystem and the collapse of high-biomass blooms leading to anoxia. As part of the Benguela Current Large Marine Ecosystem Programme, a bio-optical buoy has been developed for monitoring HABs in the region, providing both real-time and time-series data. Considerations in developing the buoy were that it should be small, cost effective and robust, allowing for field calibration of the sensors and servicing from a small boat. The instrument package on the buoy consists of two hyperspectral radiometers (providing remote sensing reflectance), a thermistor chain, a fluorometer and an Acoustic Doppler Current Profiler. A half-hourly acquisition regime collects data from the instruments, which are transmitted in real time using cellular phone telemetry. A website is updated with these data, when available, along with satellite data and shellfish warnings, to provide near real-time information on conditions in the area. Demonstration data from the buoy, related to observed blooms of dinoflagellates and the ciliate Mesodinium rubrum, are presented.