The roles of vision and the lateral-line system in fish-screen avoidance behaviors were investigated in Sacramento splittail (Pogonichthys macrolepidotus). Fish were viewed swimming in front of water-diversion-type fish screens in a laboratory flume during the day (lit condition) and night (darkened condition, using infrared equipment). Streptomycin-sulfate treatments were used to block the fish’s lateral-line systems. Lateral line neuromasts were labeled with 2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide (DASPEI) to assess the streptomycin treatment’s effectiveness. Splittail contacted the screens infrequently during the day, but contacted the screens significantly more often during the night. Also, in darkened conditions, streptomycin-treated splittail contacted the screens significantly more often than did control fish. Furthermore 60 % of the streptomycin-treated fish became impinged (stuck) to the screens during night experiments, compared to 15 % of the untreated fish. These findings suggest that splittail use their lateral-line system to detect and avoid objects (screens) in the absence of vision. Splittail displayed no response to stimuli generated from a piston-driven vibrator mounted to the center of the screens. Our findings are the first to show how fish can use different sensory systems to detect and avoid fish screens in the presence or absence of light, and they should benefit fisheries and water resources managers, regarding the timing of water extractions through screened water diversions.