As a migratory fish, the eel is particularly threatened by obstacles on waterways. One of the ways to mitigate entrainment of downstream migrants into the turbines of hydroelectric facilities, would be to predict the runs and behavior of eels according to environmental parameters. Here we investigate the link between migration peaks and river discharge and hypothesize that the results will vary according to the geographical and time scale at which the phenomenon is observed. This would not only be useful to develop specific schedules for power generation, but also to optimize the efficiency of bypass systems.