The levels of arsenic and mercury of fish samples collected in the water reservoirs El Granero, Las Virgenes y La Boquilla were determinate by atomic absorption spectrometry with hydride generator. The accuracy of the method was determinate by certified reference material (NRCC-DOLT-3 Dogfish Liver). Three factors were studicd and their infiuence on the concentrations of arscnic and mercury in fish: water reservoir, spccies and tissue. The data were analyzed using analysis of variante (ANOVA) considering the sources of variation caused by the factors and their interactions, making comparison of means tests using Tukcy's test when significant di fferences were detected by ANOVA.