aim: constructed wetlands (cws) have shown to be an efficient way for removing nutrients from wastewaters. however, a negative effect is the emission of greenhouse gases (ghgs). methane (ch4) is a ghg released from the organic matter degradation under anaerobic conditions by methanogenic bacteria. in cws, the excessive nutrient inputs may stimulate both primary production and methanogenesis and then affect the overall cost-benefit balance of this system. here, we assessed the role of cattail stands (typha domingensis pers) on ch4 concentrations in eutrophic and mesotrophic constructed wetlands. methods: cws were filled with water and sediment colonized by the aquatic macrophyte typha domingensis pers from two tropical freshwater lakes, one mesotrophic and another eutrophic. results: our results showed consistently higher ch4 concentrations in waters and sediment in the eutrophic cws than in the mesotrophic cws (two times), indicating a positive influence of eutrophication on methanogenesis. conclusion: in conclusion, ch4 emissions from tropical cws demand to be considered or even mitigated in any use of this system.