After a brief survey of the major theories on suspended-load diffusion under different flow conditions, we present here an analytical study on the diffusion of suspended load in unsteady open-channel flows. The histograms of suspended load and of flow discharge in rivers are examined, and the concept of sediment-wave celerity is introduced. It is noted that discussed here is but a small and humble step toward understanding the much complex phenomenon of suspended-load diffusion in unsteady flows.