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Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Avenue, Room 1000, Portland, OR 97204

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What is a Watershed?

Oaks Bottom wetlandA watershed is an area of land within which water from rain or snow drains into a body of water, such as a river, lake or ocean.

Portland is part of the Willamette River and Columbia River watersheds. Within the City of Portland, the land is divided into five watersheds, or areas that drain to major local streams and waterways:

Each of these watersheds is further divided into smaller drainage areas called subwatersheds.

Over the past 150 years of development, Portland grew from what once was native forests, wetlands and grasslands to an urban environment. Rain once fell on a dense tree canopy and most of it soaked into the soil to recharge groundwater. Some of it flowed naturally into streams and rivers, providing cool, clean water for fish and wildlife species. Now rain flows over roofs, parking lots and streets, becoming stormwater runoff that can pollute rivers and streams, damage habitat and cause nuisance flooding.

The Portland City Council adopted the Portland Watershed Management Plan in 2006 to guide the city’s efforts to protect and restore watershed functions, recognizing that while it is not possible to recreate pre-development conditions in an urban environment, we can work together to improve ecosystem health for the people and wildlife that live here.


A healthy urban watershed has hydrologic, habitat, and water quality conditions suitable to protect human health and  maintain viable ecological functions and processes, including self-sustaining populations of native fish and wildlife species whose natural ranges include the Portland area.” (Portland Watershed Management Plan).


For more information about watersheds in general, and what communities around the country are doing for watershed health, visit the Environmental Protection Agency’s website.