The present disclosure includes an interface sensor for a sedimentation plant, the interface sensor including: a sound emitter configured for generating at least one first acoustic signal with a first frequency and for generating a second acoustic signal with a second frequency different from the first frequency; a sound detector configured for detecting at least one first signal response of the first acoustic signal and a second signal response of the second acoustic signal; and a control unit, wherein the control unit is connected to the sound emitter and the sound detector and is configured to evaluate the first signal response and the second signal response, to determine a floor distance, a sediment distance, a sediment thickness and a water level distance based on the first signal response and the second signal response, and to determine a water level based on the floor distance and the water level distance.