Multiphase radionuclide measurements on Ottawa River waters are reported for the period October 1984 to March 1986. Numerous radionuclides are present in detectable amounts in raw, drinking and centrifuged waters as well as in suspended sediment and water filtration plant floc samples. The sediment/water partitioning behavior of these radionuclides is also reported. The prevailing low particle flux allows rapid migration of radionuclides through the system. Most of the 9~ in the river derives from its fallout inventory in the watershed rather than from the Chalk River Nuclear Laboratories (CRNL). On the other hand, fallout and CRNL-derived ~37Cs appear to contribute equally to the prevailing levels of this radionuclide in the river. The data also suggest that the prevailing levels of the naturallyoccurring 226Ra impart more dose than 9~ insofar as the radiological quality of the drinking water is concerned. Many of the radionuclides are removed by the floc during filtration of the receiving waters. Though their removal efficiencies cannot be precisely defined from the currently available measurements, the results show that processes other than simple association with suspended sediments may also play significant role in the retention of some radionuclides by the floc.