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Over-water nests of diving-ducks were located by flushing the hens, which would leave the nests at the approach of a boat. A time-sampling method was used to measure nest production with the assumption that all but a small percentage of ducks nesting in emergent marsh vegetation will locate their nests within 20 yd (18.3 m) of open water. Markers were set at the start and finish of each sample and an outboard motorboat was operated at a set speed for a predetermined period immediately adjacent to the edge of vegetation. Forty 10-minute samples were randomly established in 1949, but these were changed to twenty 20-minute samples at a faster speed in 1950 and 1951, thus covering more nesting habitat. Twenty-eight of the 147 unsuccessful nests were deserted, but no mention was made of losses possibly caused by the investigators.