SR 529 - Steamboat Slough - Mitigation Site - History

A graphic showing three stages of development along Steamboat Slough near SR 529 and I-5 - the 1800s, 1938 and 2017.

Mid 1800s – The site is an estuarine habitat, where saltwater and freshwater mix and provide habitat for young salmon.

Late 1800s – Local industry creates a diking system to support business uses.

1920s – Pacific Highway (now the southbound lanes of SR 529) is built.

1950s – The northbound lanes of SR 529 are built.

1969 – Interstate 5 opens in the area. Material is dredged from Steamboat Slough to raise the ground level between SR 529 and I-5 near Marysville. The higher ground level meant the only water on the site was from runoff instead of estuarine (a saltwater and freshwater mix).

2019 – A WSDOT project to remove the dredged material and dikes, along with planting native vegetation, will allow the property to return to its natural estuarine state, like much of the land west of the site and just east of I-5.