From 26 October to 2 November 2018, in situ measurements of dissolved methane concentrations were carried out in the water column of the Maethang irrigation reservoir by three scientists from the iEES Paris joint research unit (Sylvain Huon, Véronique Vaury, and Jean-Louis Janeau). Water and gas samples were also collected to perform stable carbon isotope measurements and control the reliability of in situ measurements by Frédéric Guérin at the GET laboratory in Toulouse. These data, together with the monitoring of environmental parameters in the water column and the analysis of 92 sediment cores recovered in February 2018, will help to better constraint the extent of carbon storage in bottom lake sediments with respect to greenhouse gas emissions in a representative of many (over 300) agricultural reservoirs of Thailand. Linking carbon cycling with land use and management on the adjacent watershed, will also support solutions involving users and managers for a sustainable management of water resources.