The greenhouse gas emissions of CH4, N2O and CO2 from a tropical reservoir and a tributary river that supplies it were measured from 2015 to 2019 using a GC-FID/µECD method. The chromatographic technique was used with a configuration of a methanizer and two specific columns, by direct injection of the gaseous samples using the floating static chamber as a field sampling method. The parameters analysed for the chromatographic methodology validation were selectivity, linearity, detection limit and quantification, bias (as a practical assessment of trueness), precision and uncertainty. These parameters were found to be satisfactory. The results showed a low deviation of the analysed data throughout the period evaluated.