This work studies mercury contamination to gold-mining activities in the "Parque Nacional y Area Natural de Manejo Integrado Cotapata". The mining area takes place on the head of a subandina river basin, the Chairo and Huarinilla rivers, affluents of the Coroico river. Both run through the protected area and pass through the Chairo Village. The mercury concentratons were determined in suspended solids and fishes that were collected in the area of Cotapata National Park. The water samples were collected in 5 points of the study area and were processed carefully - ultraclean protocols were used (Ahlers et al, 1990). The mercury analysis results obtained in suspended solids in 2 points of the Chairo River head 4 and 15 micrograms/g. The obtained values in bottom sedminents are 11,5 micrograms/g in the river basin and 0,41 micrograms/g in the Chairo and Huarinilla rivers ; in the fishes in the Huarinilla river the average concentration is 0,142 micrograms/g. So here is a beginning of a contamination risk by mercury in the Chairo and Huarinilla rivers. (Résumé d'auteur
