As part of a larger regional effort during 2004, surveys of Harlequin Ducks were conducted during pair season and brood season in Glacier National Park, with special focus on Upper McDonald Creek. In addition, pair surveys were conducted on Fish and Fern creeks near the southwest end of McDonald Lake, and brood surveys on Saint Marys River, and Reynolds and Paradise creeks east of Logan Pass. An all-day survey of Upper McDonald Creek on 9 May resulted in a count of 30 Harlequin Ducks (10 pairs and 10 adult males), the largest one-day count of the year. Another pair was present on Fish Creek. In August brood season, three broods (two with hens) were captured and banded (13 birds total); a fourth brood of seven (with hen) was observed on McDonald Creek several days after the banding operation. Thus, at least four broods of Harlequin Ducks were produced on Upper McDonald Creek in 2004. No birds or broods were seen on Reynolds and Paradise creeks, or Saint Marys River. Maximum one-day pair (ten) and total brood counts (four) in 2004 were the largest for Upper McDonald Creek since 1997 and 1992, respectively. These counts contrasted with Harlequin Duck productivity on the four monitored Lower Clark Fork streams in the Noxon area, which apparently produced only two broods in 2004 (the eight-year average from 1992-1999 was 4.6 broods). Thus it appears that good years and bad years for Harlequin Ducks are not necessarily synchronized across northwestern Montana. McDonald Creek continues to be an important Montana breeding stream for Harlequin Ducks.