Over 1 million dams exist worldwide. These structures have numerous environmental effects, and there is no shortage of research on the various ecological consequences of dams. But there is another major threat arising from dammed waters: the release of greenhouse gases. For this episode of BioScience Talks, we spoke with Dr. Bridget Deemer of the US Geological Survey. Deemer and her colleagues recently embarked on a systematic effort to synthesize reservoir greenhouse-gas data. The results, described in BioScience, point to reservoirs as a substantial yet often unrecognized source of greenhouse gases. Read the article discussed on the show. Keep up with Dr. Deemer's research. Subscribe on iTunes. Subscribe on Stitcher.