The environmental monitoring program conducted by Argonne National Laboratory for radionuclides in effluent and surface water is described and the results for the past six years are summarized. Small amounts of several radionuclides have been present in Argonne wastewater, and are consequently detectable in the stream that receives this water. The most abundant of these is hydrogen-3, whose average concentration in the stream during this period was about 3000 pCi/litre, equivalent to 0.1 percent of the drinking water standard. The distribution of plutonium and neptunium between stream water and particulate matter was studied. Plutonium tends to be relatively insoluble and become associated with the sediment, while most of the neptunium is in solution. This difference in behavior should be taken into account in designing environmental sampling and analytical programs and in dosimetric evaluation of effluent releases.