Plutonium concentrations in the bed sediment of reservoirs (Great Western Reservoir, Standley Lake, Cherry Creek Reservoir, Marston Lake, and Ralston Reservoir) in the environs of the Atomic Energy Commission Rocky Flats Plant were determined by dredge and core sampling. Great Western Reservoir and Standley Lake were sampled during October, 1973; the other three impoundments during April, 1974. The baseline level of plutonium-239 in bed sediment attributable to worldwide fallout was found to be < or = 0.10 pCi/gram (dry weight). Correspondingly, the maximum concentrations in the top layer of sediment in Great Western Reservoir were approximately 4.0 pCi/gram (dry weight). The thickness of the layer of plutonium-contaminated sediment in the reservoir was 5 cm or more at most sampling stations. Through 1973, Great Western Reservoir received liquid wastes (plutonium-bearing) from the Rocky Flats Plant via the tributary stream, Walnut Creek.