As rivers transport water and sediment across Earth's surface, they radiate elastic and acoustic waves. We use seismic and infrasound observations during a controlled flood experiment (CFE) in the Grand Canyon to show that three types of fluvial processes can be monitored from outside the channel. First, bed-load transport under conditions of evolving bed mobility is identified as the dominant seismic source between 15 and 45 Hz. Two lower-frequency seismic bands also excited by the CFE exhibited greater power increases and are consistent with source processes related to fluid rather than sediment transport. The second fluvial seismic source is inferred to be fluid tractions on the rough riverbed, which drive the maximum seismic power increase at 0.73 Hz, but do not excite infrasound. Waves at the fluid-air interface are suggested as a third source, which generates a common 6–7 Hz peak in seismic and infrasound responses to the CFE.