The reservoir created by the Sinnamary Dam is an anoxic environment rich in organic matter, making it conducive to mercury methylation. Bioaccumulation of methylmercury has been observed in fish. Since the fish consumed by the Sinnamary population comes primarily from local fishing, it became necessary to conduct a study to assess the health impact. A cross-sectional survey was conducted in November 2001 with the primary objective of assessing mercury exposure among residents living downstream of the dam and validating the estimates from the 1994 survey conducted by the RNSP. To this end, a hair sample was collected to measure mercury levels. The results show that few people have mercury concentrations exceeding 10 μg/g of hair, the threshold value recommended by the WHO. These exceedances affect 5% of the surveyed population, 6% of adults, 2% of children, and no women of childbearing age. The results confirm a relationship between mercury concentration and fish consumption. In particular, the consumption of river fish is strongly linked to high mercury concentrations. Analysis of the factors influencing mercury exposure further shows that a traditional lifestyle, based on the consumption of fish and game from the forest, is significantly associated with high mercury concentrations in hair. (Author’s summary).