Mercury levels of fish in Tucuruí hydroelectric reservoir and in River Mojú in Amazonia, in the state of Pará, Brazil

High mercury (Hg) levels were found in fish of Tucuruí reservoir and River Mojú polluted by mercury due to gold mining activities. The highest Hg concentrations were measured in predatory fish (1.3 ± 0.89 mg/kg, N = 121), intermediate values in planktivorous and omnivorous fish (0.32 ± 0.20 mg/kg, N = 89) and the lowest values in herbivorous fish (0.11 ± 0.11 mg/kg, N = 14). Tucuruí reservoir is thoroughly polluted by mercury. Only the side basin of Caraipé had a little less mercury in fish. Tucunaré (Cichla temensis) and pescada (Plagioscion squamosissimus) seemed to be good indicator species for mercury pollution in Tucuruí reservoir. In Tucuruí reservoir and in River Mojú, 92% and 100%, respectively of the predatory fish samples contained more than 0.5 mg Hg/kg, which is the safety limit for Hg in Brazil. The consumption of large predatory fish from the study area should be restricted to avoid the risk of methylmercury poisoning in humans.