In this study we investigate how fish approach a fish ladder by fine scale (2D) acoustic tracking. The behaviour is linked to hydraulic data and bathymetry in the area around the fish ladder entrance. In the village Rotselaar (Belgium), fish in the river Dijle are obstructed by an old mill. The mill has changed into a hydropower station many years ago and is equipped with one turbine with a max. capacity of 5 m³/s. A fish ladder around the mill facilitates upstream fish migration. The ladder is located perpendicular to the river and close to the outflow of the turbine. The study runs over several years and the flows will be altered to study before and after upstream fish migration near the fish ladder and the turbine.The study is part of the RIBES project (River flow regulation, fish BEhaviour and Status; https://www.msca-ribes.eu/). RIBES wants to find innovative solutions for freshwater fish protection and river continuity restoration in anthropogenically altered rivers. This includes improving fish ladder efficiency by studying how fish react to the flow when approaching a fish ladder.