The drainage network of the Odiel river (SW Spain) is intensively contaminated by acid mine drainage (AMD). The Odiel river basin drains the materials of the Iberian Pyrite Belt (IPB), a large metalogenic province hosting numerous, large scale massive sulphide deposits. The aim of this study is to quantify the contaminated load transported by the fluvial network of the Meca river, tributary of the Odiel. The Meca river is strongly affected by acid lixiviates coming from Tharsis mine, located in the northern area of the watershed. It is regulated by a reservoir which water has a pH close to 4 and high contents of Al and other toxic metals. By means of several samplings the quality of water has been obtained. Due to the shortage of stream flow gauges, a hydrological model is used to obtain flow rate data. The dissolved transported load is calculated from the correlation between contaminant concentration and flow rate. The results show that the Meca river transports enormous quantities of dissolved contaminants: 418 ton/year of Al, 121 ton/year of Zn and minor quantities of other metals. The comparison between average element average concentrations calculated from these results and the reservoir water quality shows a good agreement