Prior to 1915 both Oregon City and West Linn got their drinking water from the Willamette River. After a typhoid outbreak in 1913, the Oregon City Commission formed the Pure Mountain Water League and directed it to find a new source of drinking water. The League identified the South Fork of the Clackamas River. In March of that year the Oregon City Commission accepted West Linn’s request for one-third share in the project. Representatives from both Cities were selected and the South Fork Water Board was created.
In 1915 twenty-six miles of 18” pipe of was constructed to a site near Memaloose Creek, about 3,000 feet from the confluence of the South Fork and the main stem of the Clackamas River. This pipeline became known as the Mountain Line. The first water began to flow by gravity through the system on October 7, 1915, supplying three million gallons per day. The only treatment at this time was chlorination.
In 1939-40 South Fork Water Board joined with the federal Works Project Administration to extend a 24” line upstream from Memaloose Creek to a point above the high falls (pictured) by means of a series of tunnels that were hand drilled through granite cliffs. This effort raised the system's intake 1,000 ft, increasing the water pressure and capacity available to users of the system.
In the 1950s the Mountain Line could no longer support the growth of the two cities, and voters decided to build a filtration plant on the Clackamas River. That plant was dedicated in 1958 and is still operating today. The Mountain Line was in use until 1985, and since then the lower Clackamas has supplied all of the water for Oregon City and West Linn.
In 1994 South Fork Water Board sold bonds to pay for the construction of a new raw water intake, which went into operation in August of 1996. This intake pumps water from the Clackamas River almost 2000 ft in distance and 300 ft in elevation to the water treatment facility.
In 1996 the City of West Linn purchased the remaining ownership and since then the two cities have been equally represented on the Board.