Lakes in the Amazon basin contain large amounts of organic carbon derived from primary production in the lakes and on land bordering them. Biological oxidation of this organic carbon leads to waters supersaturated in carbon dioxide (CO2) and evasion of the CO2 to the atmosphere. The total amount of carbon released to the atmosphere from Amazon lakes, rivers, and wetlands is estimated to be similar to the amount sequestered by Amazon forests. Complementing other measurements, Rudorff et al. measured the seasonal and spatial variability of the dissolved CO2 concentration and estimated CO2 emission from a large lake in the Amazon floodplain.