Scappoose Bay is part of the widest flood plain reach of the upper Columbia River estuary. This area is composed of multiple islands, sloughs, tide channels, wetlands and seasonal ponds, as well as terraces and rocky outcroppings. Milton, and North and South Scappoose Creeks are major tributaries to Scappoose Bay, which flows into Multnomah Channel just upstream of its confluence with the mainstem of the Columbia River.
The watershed is home to Oregon ash and black cottonwood forests, along with wetlands composed of wapato and bulrush. However, the construction of levees, roads and drainage ditches, along with floodplain filling, has disconnected many of the side channels from the river. Hydrologically, this reach of the Columbia is tidally influenced, but is also significantly backwatered by the Columbia River freshets in the spring and early summer.
A majority of the Columbia Basin’s anadromous salmon populations pass through this area during their migration to and from the Pacific Ocean. Coho, Chinook, steelhead, and cutthroat trout can be found in Multnomah Channel and the Bay’s major tributaries. Although there has been a significant decline in their numbers from historic populations, recent and ongoing efforts are improving access to restored habitats.
As one of the most important stopovers of the Pacific Flyway, the area also supports numerous populations of waterfowl, migrating shorebirds, and neotropical songbirds, as well as raptors. The waterway channels and riparian areas also provide habitat for a variety of amphibians and reptiles, including red-legged frogs and northwestern salamanders.
Milton, and North and South Scappoose Creeks are the major subwatersheds draining into Scappoose Bay. McNulty Creek and Honeyman Creek are smaller drainages that also contribute to Scappoose Bay, and Jackson Creek flows through the Scappoose Bay Bottomlands into the Multnomah Channel above the Bay.
The upper watersheds are dominated by high gradient, confined, and small streams, and are generally forested. The mainstem reaches of the major streams generally flow through low-gradient valleys and are unconfined, with the exception of stretches of larger tributaries confined within ravines, usually in the upper reaches. Much of the adjoining acres of these streams are in agriculture use and have lost much of the important riparian vegetation. The lower portions of the subwatersheds are classified as lowland floodplain and were historically heavily influenced by annual flooding along the Columbia River.
Find more details about the Scappoose Bay Watershed and our plans designed to improve the health of the watershed through specific, prioritized restoration actions.
- 2018 Strategic Action Plan
- Sauvie Island and Multnomah Channel Bottomlands Conservation
- 2014 State of the Watershed
- 2000 SB Watershed Assessment
- Water Quality and Salmon Monitoring in the SBW
- Resource Studies:
Partner Resource Studies:
- Coming soon