We employ a comprehensive (1900–2009) stream discharge gauge database to analyze the tidal impacts on inland streams. Our analysis reveals a strong lunar phase signal in stream gauge time series across the conterminous United States such that the largest tidal impact on inland rivers is evident at or just after the quarter moon (halfway between full and new moons). As an explanation, we examine precipitation using the Historical Climate Network precipitation dataset. Verifying early studies’ results, we find an equivalent well-defined lunar phase relationship with precipitation such that the largest tidal impact on precipitation generally occurs just before the quarter moon. Our results imply that inland precipitation is influenced by lunar tides and forces the lagged runoff evident in stream gauges. The lunar-induced periodicities in the stream gauge network, evident far from ocean-induced tides, may also influence flooding, as well as water management and power generation.