It flows northwest entering Port Gardner Bay, part of Puget Sound, between Everett and Marysville.

Measured at Monroe, the Snohomish River has an average annual flow of 9,500 cubic feet per second (270 m3/s).

From Snohomish, the river continues northwestward through a broad floodplain, forming the eastern boundary of the city of Everett.

[8] The lower Snohomish River was a site of major industry during the 20th century that contaminated the area with various pollutants, including oil and fuel products from former mills and factories.

An ore smelter operated by ASARCO contaminated soil and groundwater near the Snohomish River with arsenic.