Local detectability is one of the key aspects in establishing functional fish passage structures. Herein we present a novel method as extension of the habitat analysis System CASiMiR for assessing the attraction flow towards a fish pass. The method combines state-of-the-art 2D-hydrodynamic-modelling with recent f indings from ethohydraulics. Computed flow velocity fields are evaluated using the "ethohydraulic diagram" allowing for the determination of regions with flow velocities below rheotaxic thresholds as well as those exceeding the critical velocity of target fish species. Additionally, computed pathlines using an agent-based modeling approach allow for the analysis of possible upstream migration paths assuming ideal rheotaxis. The method allows for an adaptive fish passage design including the optimization of an entrance position and geometry in conjunction with the amount of attraction flow.