ABSTRACT: We analyzed the spatial and temporal variability of seston parameters at 4 locations in the Ría de Ares-Betanzos (NW Spain) over 5 yr. Seston content was higher in the inner part of the ría and during winter, while seston quality was higher in the outer part of the ría with maximum values during summer, and exhibited a marked relationship with water circulation. Inter-annual differences were detected only in the organic content of seston (which was not always well-correlated with chlorophyll a), and only at some locations. Seston quality had the strongest relationship with meteorological factors, and was the only variable that was consistent at the 4 sites within the embayment. This led us to develop an empirical model that explains the spatial-temporal variability of seston quality in terms of wind stress and river discharge.