The Olifants River System has been subjected to prolonged and cumulative ecosystem stress as a result of human activities such as mining, agriculture, industry and human settlements in the catchment. The objectives of the study were to assess pollution in the water and sediment by seven heavy metals and possible sources of pollution in two major tributaries of the Olifants River: the Blyde and Steelpoort rivers. The mean concentrations of the seven heavy metals in the water were low. The mean concentrations in the sediments were very high in both rivers. The results showed high levels of As and Mn in the Blyde River, and Cr, Fe, Mn and Zn in the Steelpoort River. The As and Mn in the Blyde could be from fertilizers, pesticides and other agricultural products, and Cr, Fe, Mn and Zn in the Steelpoort could be mainly from mining and agricultural discharge. The sediment analyses indicated a highly significant difference between the two rivers with the exception of As and Pb. The results of the enrichment factor (EF) and geo-accumulation index (Igeo) indicated pollution by Mn and Cr in the Blyde, and Cr, Fe, Mn, Ni and Zn in the Steelpoort. Thus, the results showed that there was a greater accumulation of heavy metals in the sediments of the Steelpoort than in the Blyde. The study demonstrates the need for a holistic approach to monitor pollution in the Steelpoort and a comprehensive strategy to prevent health risks in humans – especially communities that rely on the river for water and food.