A smooth water surface acts as an acoustic mirror, deflecting echolocation pulses away from the bat rather than back to it. That makes still water an unusually quiet background but also hides anything beneath it. Noctilio leporinus exploits the geometry rather than fighting it.
The bat detects the ripples, jumping fish and fin tips that break the surface, which stand out sharply against the mirror-flat return. It then makes a raking pass, dragging enlarged hind feet with long recurved claws through the top few centimetres of water. Captured fish are transferred to cheek pouches and chewed in flight. The species also takes insects from the surface and on the wing, and diet varies with season and site.
A persistent overstatement is that the bat detects fish below the surface directly. Experiments indicate detection relies on surface disturbance and on wires or objects protruding above the water; a fish that leaves no trace at the surface is not located.