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The City of Portland, Oregon

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Ave, Suite 613, Portland, OR 97204

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Portland's Municipal Stormwater Permit

  • Effective Stormwater Management Protects & Enhances Our Waterways

  • BES Monitors the System to Detect & Eliminate Illicit Discharges

  • Storm Sewers Meet Our Waterways at Outfalls

  • BES Maintains Over 440 Miles of Storm Sewers

  • Green Infrastructure Reduces Peak Flows & Treats Stormwater as it's Collected

This page is moving! Please visit our new MS4-TMDL Program page at for current content.

The City of Portland and its co-permittee, the Port of Portland, implement stormwater management programs under an Oregon Department of Environmental Quality (DEQ) permit issued under the federal Clean Water Act. The permit is formally called the Phase I National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) Discharge Permit.

It is referred to as the NPDES permit, MS4 permit, or municipal stormwater permit.

DEQ issued the first Portland permit in 1995 and renewed it for a second term in 2004 (with modifications in 2005). DEQ issued the final third-term permit on January 31, 2011.  The permit expired on January 30, 2016 and has been administratively extended by the DEQ. 

The permit requires each co-permittee to develop and implement a Stormwater Management Plan (SWMP) that describes measures the co-permittee will implement throughout the permit term to control pollutant discharges to the storm sewer system. 

TMDL Implementation

Click here for information about the City's TMDL Program that includes key strategies the City uses to address pollutants from nonpoint sources and impaired waterways.

Monitoring Plan

Current Monitoring Plan for Stormwater and Surface Water Sampling by the City of Portland in Compliance with MS4 Permit Requirements

2015 MS4 Permit Renewal Application

2015 application for the renewal of Portland's Phase I NPDES MS4 Permit, which was issued in January 2011.

MS4 Permit

A link to the City of Portland's 2021 Phase I Municipal Separate Storm Sewer (MS4) NPDES Permit.

Stormwater Management Plan

The 2011 SWMP describes best management practices and programs the City implements to comply with the MS4 NPDES Permit and reduce pollutants from the MS4 to waters of the state.

Hydromodification Assessment

November 1, 2014 report to the Oregon Department of Environmental Quality