Measurements are presented for the rate of atmospheric reaeration in open-channel flow under different conditions of depth and bed roughness. A 2k factorial design was employed for the estimation of both depth and bed resistance factor effects upon stream reaeration. Consistent results indicated that stream reaeration is primarily controlled by water shear, but that different modes of instability generated by a combination of depth and strip roughness levels might prevail for different boundary roughness conditions, and as a consequence, differently affect the reaeration coefficient.