Methane (CH₄) emissions from freshwater reservoirs are increasingly recognized as significant contributors to global greenhouse gas budgets. However, the impact of invasive macrophyte decomposition on these fluxes remains understudied. In Las Curias Reservoir, Puerto Rico, the biological control of the invasive aquatic fern Salvinia molesta resulted in the in situ deposition of approximately 3,449 tons of wet biomass. This study investigates how such biomass accumulation affects CH₄ fluxes and water chemistry from July 27 to August 10, 2024, through measurements taken at 30 unevenly distributed sites, focusing on areas with a high presence of Salvinia molesta. Diffusive emissions were measured using floating chambers, while ebullitive fluxes were evaluated using passive gas traps. On-site water quality parameters were assessed with a portable probe, and additional water samples were collected to quantify dissolved nutrients, metals, and other variables. Sediment analyses involved measuring organic matter percentage and conducting anoxic incubations to assess methane production potential. Initial findings show notable spatial variability, as the lacustrine zone, where Salvinia molesta is most prevalent, accounts for 62.44% of total CH₄ emissions, primarily driven by sediments containing over 49% organic matter. These findings suggest that greenhouse gas fluxes in this reservoir are primarily influenced by the abundance of Salvinia molesta biomass in the sediment.