The Ensenada de San Simón is the inner part of the Rı́a de Vigo, one of the major mesotidal rı́as of the Galician coast, NW Spain. The geochemistry of its surface sediments, and the river sediments which drain into it from a granitic and metamorphic hinterland, are described. Multivariate statistical analysis of the sediment compositions (using ridge regression and mixture-modelling) enabled the major- and trace-element distributions to be accounted for in terms of both natural and anthropogenic sources: Between 60 and 80% of the Cr, Cu, Ni, Pb and Zn concentrations of the bottom sediments of the Ensenada can be explained by sediment input from the combined R. Oitaben and R. Verdugo, the R. Redondela and faecal matter from mussel rafts, but there is additional enrichment towards the mouth of the Ensenada. This enrichment is attributed to marine water entering the Ensenada from the polluted industrial areas of the adjacent Rı́a de Vigo. It is suggested that these metals are carried landwards in solution by the tidal incursion of marine water (the volume of which, on an annual basis, greatly exceeds that contributed by the rivers). Although the incoming marine waters may also be important in supplying Pb to the outer Ensenada, this element may also be delivered by land run-off, or by windborne vehicular emissions to the Ensenada as a result of the surrounding network of roads and a road bridge over the Estrecho de Rande.