River water was collected from the Tonle Sap-Bassac Rivers (Cambodia), the Citarum River (Indonesia), the lower Chao Phraya River (Thailand) and the Saigon River (Viet Nam) in both dry and wet seasons. Nineteen trace metals were analysed (Be, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, Ba, Tl and Pb). Dissolved metal concentrations of most target elements exceeded the background metal concentrations by multiples of 1.1 to 87.8. Cluster and stable lead isotope analyses confirmed metal contamination in Southeast Asian rivers is anthropogenically linked. For example, discharges of wastewater, road runoff and street dust. Quantitative risk assessments of metals in the rivers showed potential toxicity of additives and negative effects of metal mixtures at all sampling sites in all areas studied. The contribution of particular metals to the cumulative criterion units (CCU) score depended on their concentrations. Al in all study areas contributed the highest percentage (72% to 85%) to total CCU scores. Cd, Cr, Cu, Pb, Ni, Zn, As and Se had lower contributions (<1% to 19%).