Geography

Seventeen miles of the 300-mile long Willamette River flow through Portland, connecting the city to the rest of the Willamette Valley and the Columbia Basin. Almost all of Portland’s land drains to the Willamette River. Some areas first drain to smaller local streams or waterways including Johnson Creek, the Columbia Slough and Tryon Creek, which then flow to the Willamette.

Locally, we define Portland’s Willamette watershed as an area of the city that doesn’t first drain to one of these other local watersheds. Portland’s Willamette watershed runs along the river from just south of the Sellwood Bridge north to the confluence with the Columbia River at Kelly Point Park, and from the West Hills to some neighborhoods east of I-205. For watershed planning and monitoring purposes, Portland’s Willamette watershed is often divided into three parts:

• The mainstem of the river and areas immediately adjacent to it.
• Willamette tributaries – including the West Hills and Forest Park, where many miles of surface tributary streams still flow through forested areas and neighborhoods, then to the Willamette River. Stephens Creek, Balch Creek, and Tanner Creek are examples.
• East side and west side neighborhoods including downtown Portland and some of Portland’s oldest and most dense residential neighborhoods, where the historic streams were long ago filled in or piped and paved over by development.

Stormwater Management

Portland's combined sewer system collects most of the stormwater runoff from the large developed areas of Portland’s inner southeast, northeast, and the central city and carries it to the Columbia Boulevard Wastewater Treatment Plant in north Portland, which treats it and discharges it to the Columbia River.

Portland's separated stormwater system manages stormwater from other parts of Portland’s Willamette watershed. In some areas, stormwater flows into tributaries that drain to the Willamette River.

Learn more about stormwater management in Portland.

Water Quality and Watershed Conditions

The river is a significant place for people to enjoy nature and recreation. Water quality is important, both because of the impacts to fish and the aquatic food chain and because of human contact with the river. Completion of the Combined Sewer Overflow (CSO) Program in 2011 reduced CSOs to the Willamette by 94%, a major improvement that has encouraged much greater activity in and around the river.

Significant challenges to improving river conditions still remain. In the mainstem Willamette, channel modification, disconnected or filled floodplains, and hardened riverbanks have resulted in lost habitat function and flood storage capacity. Bacteria, toxics and high temperature remain the primary water quality concerns. Historic sediment contamination has led to the designation of Portland Harbor as a Superfund site.

In west side tributary streams, development has created more impervious surfaces (streets, roofs and parking lots) and reduced vegetation. This has led to altered hydrology (the flow of water over land and in streams), degraded water quality and degraded in-stream and riparian habitat.

Despite these challenges, valuable pieces of habitat and a diversity of fish and wildlife still exist in this watershed. Several species of salmon and other native fish migrate through the city in the Willamette River. Portland’s forests, wetlands, and other habitats are critical for both fish and wildlife for feeding, refuge, rearing and mating, and for providing clean water sources. Urban habitat features such as ecoroofs, parks and street trees help connect our upland natural areas to the river.

Environmental cleanup, stormwater management, protecting existing resources and watershed restoration actions contribute to the city’s long-term vitality with a prosperous working harbor and a clean and healthy river for all Portlanders.

Learn more about the challenges and the benefits of healthy urban watersheds, and about specific issues and actions in the Report Cards for the Willamette River and Willamette Tributaries.

Find more detailed characterization information about the Willamette and its subwatersheds on the Plans, Studies and Reports page.