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Human disturbance of summer-molting ducks may adversely influence their selection of molting lakes. Disturbance by humans on Swan Lake was negligible and canvasbacks (Aythya valisineria) were widely distributed on the lake in summer. Dauphin Lake, however, was actively used for recreation by boaters and fishermen and only a few hundred canvasbacks passed their flightless stage at Dauphin Lake well out in the lake far from the nearest food plants and intense boating activity. During fall, thousands of flying canvasbacks readily used the pond-weed-rich southern end of the lake where few ducks were seen in summer. Human activity in this region was no doubt less frequent during fall than summer, but canvasbacks with the power of flight may be more tolerant of disturbance. Similar circumstances could account for the paucity of summer-molting redheads (Aythya americana) at Sagemace Bay even though redheads intensively used nearby Long Island Bay. Sagemace Bay was proximal to the towns of Winnipegosis and Camperville and two roads paralleling the west and southwest shores, while Long Island Bay was relatively secluded.