Abstract: Salto de San Fernando” hydropower plant is placed at River Tormes, just upstream of Santa Teresa reservoir (Salamanca, Spain). The dam is 13 m high and it has a pool and weir with bottom orifice fish ladder to let potamodromous fish (Iberian barbel – Luciobarbus bocagei–, Nothern straightmouth nase –Pseudochondrostoma duriense– and brown trout –Salmo trutta–) overcome the obstacle. This fish ladder is being monitored since 2012: daily trapping and counting fish that reach the last pool; fish passage video recording through orifices and spillways; tagging fish (PIT, Tbar and others) and studying passage metrics (location, entrance, passage time, performance). Results have been analyzed as a function of physical –discharge, temperature, atmospheric pressure– and biological variables –species, sex, size, competition–. Downstream migration is also analyzed to locate fish routes and understand fish behavior. After every research, passage improvement options are detected, accomplished and assessed on next migration season. At this moment, this overall approach has quintupled fish ladder efficiency and it offers lot of information about Iberian fish behavior and their preference under different hydraulic conditions.