Henry Hagg Lake (also known simply as Hagg Lake) is an artificial lake in northwest Oregon, in the United States. The reservoir is an impoundment of Scoggins Creek, which drains a small portion of the eastern side of the Northern Oregon Coast Range. The lake and creek are part of the Tualatin River’s watershed in the Tualatin Valley. It is located about 5 miles (8.0 km) southwest of Forest Grove.

The lake is named for Henry Hagg, an Oregon dairy farmer who was active in local agricultural committees during the first half of the twentieth century.

Scoggins Dam was built in 1975 by the United States Bureau of Reclamation, which still owns and operates the facility. Hagg Lake contains 53,640 acre-feet (66,160,000 m) of water that can be used. Some water from the lake is used by Clean Water Services to augment the flow of the Tualatin River during the summer months to reduce the temperature and improve water quality. Other users include four cities and the Tualatin Valley Water District.

In 1967, fossilized shark remains were discovered near the lake.

• List of lakes in Oregon

• Entry for the lake in the Atlas of Oregon Lakes