Beginning about 100 years ago when the first diversion dam was built in Bull Run, the City began changing the natural flow of the Bull Run River which flows into the Sandy River. Due to a variety of causes including decreased flow from the Bull Run wild populations of Chinook and steelhead have declined 75 - 90 percent in the Sandy River Basin. The City s goal is to ensure a reliable, affordable water supply while improving conditions for ESA-protected fish. The Bureau is looking at its effect on fish populations in the Sandy Basin. Neither dam has fish ladders.
Historic habitat is flooded.
Salmon and trout generally favor habitat in wide, flat river valleys. Two reservoirs now flood much of the historic habitat. Water is warmer. As the water slows and pools up behind the dams, it absorbs heat from the sun. Salmon and trout prefer cool water.