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Coarse particulate organic mass varied seasonally and changed from autochthonous to allochthonous organic matter along a 386-km section of the Colorado River below Glen Canyon Dam, Arizona. Dam operations influenced drift components selectively throughout the hydrograph; however, ramping rate had no effect on drift mass. Eddies and pools collected similar to 50% of the main-stem drift with only detritus retained long enough to settle in pools. Coarse particulate organic drift mass was negatively correlated with stream gradient in the Colorado River. Cladophora drift packets were pulverized by rapids, which subsequently increased fine particulate organic matter at downriver sites. Tributary type (spring stream or large desert watershed river) significantly altered the mass and composition of tributary drift; however, tributaries contributed <0.1% of the total organic matter to main-stem drift. Terrestrial insects represented <0.001% of the total invertebrate mass in main-stem drift. As a result of hydraulics and suspended sediment, organic drift mass throughout the river corridor is reach specific. Longitudinal change in drift composition corresponds with a shift in fish species.