Cleaning Up the Columbia Slough’s Sediment

Photo shows waterway winding from left to right with trees, muddy banks, and piles of wood along the sides.
Environmental Services' Columbia Slough Sediment Program works closely with the Oregon Department of Environmental Quality to investigate environmental conditions in the slough and implement actions to prevent pollution and improve watershed health.

The contamination in the Columbia Slough's sediments is widespread and at relatively low concentrations. It reflects years of historic agricultural and industrial activities in the areas around the slough that contributed long-lasting pollutants to the sediments. With more than 200 stormwater outfalls that carry runoff from public streets and neighborhoods directly to the slough, the City also has a role in the cleanup of slough sediment.

The Columbia Slough Sediment Program is responsible for meeting the requirements of the state’s environmental cleanup law. The requirements are outlined in the 2005 Oregon Department of Environmental Quality Record of Decision for Slough Sediments. Since 1993, Environmental Services and the Oregon Department of Environmental Quality (DEQ) have been working together to investigate environmental conditions in the slough and implement actions to reduce contaminant discharges and improve watershed health.

Our Cleanup Approach

  • Identify and work with businesses to prevent pollution from industrial and commercial facilities.
  • Stop unauthorized and illegal discharges to storm sewers that flow directly to the slough.
  • Implement citywide actions to meet the requirements of the City’s Municipal Separated Stormwater Sewer permit and Total Maximum Daily Load Implementation Plan.
  • Install pollution reduction facilities, such as green streets and stormwater filters, to reduce contaminant levels in stormwater runoff from selected public roadways before discharge to the slough.
  • Test sediment quality and fish tissue in the slough over time to assess progress reducing pollutant levels.
  • Stop soil erosion.
  • Encourage property owners to landscape with native plants and reduce pesticide use.
  • Build and restore wetlands to filter stormwater.
  • Add native plants and trees along the banks of the slough to buffer the water from human activity.
  • Engage residents of the Columbia Slough watershed to ensure they know how they can help keep rivers and streams clean.
  • Eliminate sanitary waste overflows into the slough. In 2000, Environmental Services finished building the Columbia Slough combined sewer overflow projects, which eliminated combined sewer overflows to the slough.

Annual Report

The City and DEQ continued their ongoing collaboration to clean up the Columbia Slough in 2022-2023. Key accomplishments of the past year include:

  • Approximately 20 properties undergoing source control evaluations and/or clean-up actions to prevent sediment recontamination.
  • Stormwater treatment design is underway in 13 priority outfall basins to improve water quality and reduce runoff from selected City rights-of-way that discharge to the slough.
  • Community Engagement Liaisons representing refugee, immigrant, indigenous, people of color, and disabled communities continue to assist with City outreach efforts on the slough fish advisory. Liaisons also collected information from their communities about possible future recreational and educational opportunities in the slough.
  • The City continued to implement a wide range of source control actions to reduce pollutant discharges to the slough. Examples of source control actions include street sweeping, catch basin cleaning, spill response, erosion control, green street stormwater facility maintenance, tree plantings, site inspections, and educational tools.

Columbia Slough Story Map

The Columbia Slough Story Map provides an interactive resource for people interested in learning more about the Department of Environmental Quality's Columbia Slough Sediment Cleanup Plan. This detailed resource includes a description of the Columbia Slough sediment cleanup plan, an overview of individual sediment cleanups, and a timeline of key events.

More Information