Environmental DNA: a new technique for the inventory of freshwater species We describe the use of environmental DNA for detecting the presence of freshwater species. Often, their secretive behavior or low density prevents this. Compared with traditional methods, the presence of a species can be implied with far more certainty. This novel approach is based on the limited persistence of a species’ DNA in the environment. The DNA may come from shed skin cells, faeces or urine. By taking a water sample and analysing its DNA content, the presence or absence of a target species can be ascertained. RAVON and the French scientists who developed this technique a few years ago, have collaborated to improve the method with regard to new primers (pieces of DNA that bind and help to amplify the environmental DNA in the sample for further analysis), sampling strategy and other field practices. We give the results of a successful pilot study to detect the rare and secretive Weatherfish (Misgurnus fossilis). Using the environmental DNA technique, we were able to detect the fish in all four waters where the species was known to be at a high density and three out of four waters where it was present at a low density. No Weatherfish DNA was found in the samples of four waters in which the fish did not occur. We give an overview of the strength of the new method, as well as our goals for the future.