In the French management plan the Sea-Hope approach implemented to quantify the impacts of hydroelectric facilities to downstream-migrating European eel is based on the predictive models (i) yellow eel distribution and yearly proportion of downstream migrants, (ii) hydrology and downstream migration dynamics, (iii) hydrology and alternative passage routes at hydro facilities, and (iv) turbine characteristics and passage survival rate. To refine the second and fourth sub-models on an obstructed river with pluvial flow regime, PIT- and radio-tagged silver eels were monitored in the highly fragmented Dronne River during hydrologically contrasted years. Resulting variable escapement rates and migration speeds proved that river flow may constitute a good environmental cue triggering the timing and strongly influencing the kinetics of migration. Combined analysis of migration timing and individual migratory behavior confirmed that most of the migratory activity was concentrated in a narrow environmental window. Migration blockages were observed in unfavorable environmental conditions or following passage through turbines. Pronounced day-night activity rhythms within such a narrow environmental window make the possibilities of temporary turbine shutdowns particularly relevant. This study currently complemented by the development of large RFID flatbed antennas and the use of electromyogram transmitters should improve further elements of Sea-Hope.