SR 529 - Steamboat Slough - Mitigation Site

Project news

  • Work on this project began July 1. People traveling on SR 529 should be prepared for daytime and nighttime shoulder closures and lane reductions.
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Needs & Benefits

Restoring estuarine habitat (where saltwater and freshwater mix) is good for many species, from tiny marine organisms to orcas. It’s a nursery where young Chinook, coho, pink and chum salmon can grow before continuing their journey to the Salish Sea and Pacific Ocean.

This project – located between I-5 and southbound SR 529 just outside of Marysville – will restore nearly 11 acres of estuarine habitat. It will cut down trees that have grown on fill material placed in the area since the 1950s, lowering the land to its original level. The project will add tidal channels, then breach a dike to allow tidal water from Steamboat Slough into the area. The trees that were cut down will be placed on the site to provide additional wildlife habitat.

The work is mitigation for the I-5 Marine View Drive to SR 528 Peak Use Shoulder Lane and Interchange Improvements project, which will add a southbound I-5 on-ramp and northbound I-5 off-ramp at SR 529 and well as a peak-use shoulder lane on northbound I-5.

What to expect
People who travel on SR 529, particularly bicyclists, should plan for shoulder and lane closures as crews remove trees. People will notice that more than 100 cottonwood, fir and other trees will be cut down between I-5 and SR 529, and crews will remove fill from the site. Prior to dikes and fill being added to the area, trees did not grow in what originally was a saltwater marsh. In a few years this area will look like the surrounding saltwater marsh.


  • May 2019: Project awarded to Trimaxx Construction Inc.
  • July 2019: Work began to remove trees and fill from the area.
  • Fall 2019: Dikes will be breached and native plants will be added.


Funding for this $7.75 million project is provided by the Connecting Washington program.


Tom Pearce

Ed Kane
Project engineer

A small map showing the location of the SR 529 mitigation site.