The aim of this cross-sectional study was to estimate the prevalence of hypertension among adults (n = 841) in communities along the Madeira River in the Brazilian Amazon, prior to startup of the Santo Antônio Hydroelectric Plant. The study gathered information on sociodemographic conditions, history of diseases, habits, fish consumption, and anthropometric parameters. Logistic regression was used to calculate odds ratios and the respective confidence intervals. Among the riverine communities, 26% (95%CI: 23%-29%) of adults presented hypertension (29% in men [95%CI: 24%-33%] and 23% in women [95%CI: 19%-27%]). Factors associated with hypertension were age, BMI, and place of residence in men and age, triglycerides, and blood glucose in women. The findings can contribute to strategies for state and municipal health services to monitor and prevent cardiovascular events.