Environmental parameters recorded at three sites of the study area. Water discharge is recorded at poses weir (upstream limit, R3, source: DIREN Ile de France and Banque hydro). Temperature is continuously recorded by loggers attached to receiver R36 (Fig. 1). Oxygen was recorded occasionally at receiver R26. A horizontal double line indicates a critical oxygen concentration for fish under this value. A horizontal dotted line represents a comfortable and healthy oxygen concentration above this value. Vertical grey lines indicate the two release periods.