The metal content measured in surface sediment and suspended particulate matter (SPM) samples collected from the Ulla River estuary (NW Spain) showed evidence of contamination by Cr, Cu, Mn, Ni, and Zn, but not by Cd, Fe, and Pb. The metals are trapped mainly in the sediment of two estuary zones, just before they reach the Arosa Ria. The first zone is located at the estuary head, where estuarine mixing occurs and the SPM from the Ulla River contributes Cu, Mn, Ni, and Zn, while the Sar River discharges urban waste and Cr. The second zone is located at the estuary mouth (ria head), where a weak sediment dynamics and the presence of mussel rafts results in contamination by Cu and Cr, metals that are abundant in the SPM that manages to traverse a shallow sand bar found before the estuary mouth.