Fish can contain high levels of mercury, which can harm health when consumed in large quantities. This work aimed to assess mercury exposure and fish consumption and calculate the health risks associated with consumption of mercury-contaminated fish in the riverine communities of Baixo Amazonas area, in the Brazilian Amazon. Materials and methods: A health risk assessment was carried out according to the methodology of the World Health Organization. Weight and fish consumption data were obtained in 2022 through a structured questionnaire covering social, demographic, and behavioral variables, fish consumption and symptoms associated to Hg exposure; and blood mercury was measured. Different scenarios of Hg contamination were used. Results: 108 participants were selected, of whom 89% (n = 96) were exposed and frequently consumed fish. Fish consumption indicated that the daily intake of methylmercury exceeded the recommendation of 0.23 µg MeHg/kg for women of childbearing age and 0.45 µg MeHg/kg for adult men. In these two groups, the risk ratio was higher than 1.0; in women of childbearing age (18–49 years), the ratio was 1.8, and in adult men the ratio was 1.2. Conclusions: These results indicate that fish consumption although essential for the food and nutritional security of the riverine community, can cause significant health risks due to the consumption of mercury-contaminated fish.