The quantitative description of the aquatic space is essential for ecohydraulic modelling. It is recommended to quantify the hydraulic variety for a given flow and any area of the aquatic space by calculating the volume or surface percentages in a depth and current velocity cross-classification. This representation in the velocitydepth plane is called a hydraulic signature. HydroSignature' is a free beta software used to calculate signatures and can be downloaded at: http://hydrosignature.aix.cemagref.fr/ Its calculation principle through decomposition into finite elements is based on three different field data collecting types: (1) depthcurrent velocity measurements in unspecified locations, (2) descriptions using cross-sections and (3) use of a triangular irregular network (TIN). Using signatures in fish habitat models is recommended to avoid extrapolating outside limits when determining taxa preference during hydraulic simulations at different flow regimes.