The Willamette Basin is dotted with many small perennial lakes. Most of these were the result of shifts in old river channels and were more numerous before the arrival of settlers in the 1800s when drainage became a land use issue. The region is also the site of numerous man-made dams and reservoirs established to provide flood control, water storage, and recreation.
While many people think of "dams" in terms of large federal projects, such as Lookout Point (the reservoir with the largest maximum storage capacity in the Willamette River Basin at 477,700 acre-ft.) or Cougar Reservoir (the reservoir with the highest dam in the Basin at 519 ft. above stream level), a significant percentage of dams within the Basin are small private dams constructed primarily for purposes of irrigation.
Over 2.7 million acre-ft. of water can be stored behind the 371 dams in the Willamette River Basin: an amount equivalent to a foot of water covering over 37% of the surface of the Basin. The Tualatin River watershed has both the greatest number of dams (82) and the greatest concentration of dams within a watershed with one dam for every 8.6 miles of watershed area.
The first three dams in the Willamette River Basin were constructed in 1894 by the City of Portland for water supply purposes. While the construction of dams by local governments has proceeded over time at a low level, most federal and private dams were built between 1950 and 1980. Construction has waned since the peak in 1965-1970, and as dams have been implicated in the decline of salmon populations (through changes in river ecology and denial of fish passage) new dam construction has become controversial.
Allan, S., A.R. Buckley, and J.E. Meacham. 2001. Lakes. Atlas of Oregon, 2nd. Ed., pp. 166-167. Eugene, OR: University of Oregon Press.
Johnson, D.M., et al. Atlas of Oregon Lakes. Corvallis, OR: Oregon State University Press, 1985