[en] Because plutonium is a potentially hazardous material, extensive precautions have been exercised since Pu operations began at Mound Laboratory to carefully maintain strict control of the Pu and to prevent significant amounts from entering the environment. These precautions include elaborate facility and equipment design criteria, scientific expertise, experience, personnel training, management and operational control systems, and environmental monitoring. In spite of these precautions, in early 1974, core samples from area waterways collected and analyzed showed that ²³⁸Pu concentrations in the sediment of certain waterways adjacent to the site were above the baseline levels expected (<0.0004 nCi/g). These ²³⁸Pu deposits presented no immediate hazard to the general population in the area as indicated by the air and water concentrations which were well within accepted Radioactivity Concentration Guides (RCG) for ²³⁸Pu. Data are presented from an investigation of the extent of the contamination, the source of Pu, how it was transported and deposited in waterways, and potential hazards of these deposits to the general public