The objective of this paper is to exemplify the use of remote sensing to assess methane emissions from reservois. Man-made reservoirs seem to behave as flood plain environments that are known to make a significant contribution to tropospheric methane (CH4). Methane emissions from the flood plain, however, are variable: open water environments produce lower fluxes than those covered by floating aquatic vegetation. TM/Landsat images were used to identify aquatic habitats resulting from the construction of the three largest reservoirs in the Amazon region: Tucurui, Balbina and Samuel. These habitats are: open water, floating aquatic vegetation, and transition zone. The area covered by each of these environments was computed for each of the reservoirs. Data on the methane emission for these various environments were not available. Published data were then used to compute their likely contribution to the methane flux, assuming that the reservoir’s environments were similar to those on which the data are available.