The expansion of global aquaculture includes, among other techniques, net-pen fish farming in semiarid regions, where studies remain scarce. This study assessed the sediment geochemistry of the Rosario Reservoir in Brazil, aiming to assess the influence of net-pen aquaculture on sediment quality. Sampling was conducted in control (CTRL), cultivation (CTV), and post-cultivation (PCTV) areas, with 10 replicates each. Tests included particle size distribution, organic matter content, trace metals (Fe, Mn, Zn, Cu, Cr, Cd, Pb, and Ni), sediment quality guidelines, multivariate statistics (Pearson's correlation, similarity analysis, and principal component analysis), and geochemical indices (Contamination Factor, Pollution Load Index, Nemerow Pollution Index, and Combined Pollution Index). Sediments were determined to be clayey-silty loam, with an organic matter content of 18.76 +/- 4.27%. The highest metal concentrations occurred in the CTV (Fe, Mn, Zn, and Cr) and PCTV (Cd, Cu, Pb, and Ni) areas, with Ni exceeding sediment quality thresholds. The multivariate testing shows that aquaculture is a source of metals and organic matter. Geochemical indices revealed mostly low to moderate pollution, with localized polluted conditions. Overall, fish farming had a limited impact on trace metal accumulation. The methodological framework proved effective for environmental monitoring and management, supporting both qualitative and quantitative assessments of aquaculture-related impacts.