[en] Radionuclide concentrations in digester sludge and effluent samples from Hamilton and Dundas sewage treatment plants, located at the western tip of Lake Ontario, have been determined by high-resolution γ-ray spectrometry. The radionuclides ⁵¹Cr, ⁷⁵Se and ¹³¹I, which are used in nuclear medicine procedures, were found in sludge samples. Very low concentrations of ⁵¹Cr, entering Lake Ontario through the Hamilton plant effluent discharge, have little effect on lake water quality. (author)