The city lies on a plateau between the Snohomish River delta, which separates it from Everett and Ebey Island to the west, and the foothills of the Cascade Mountains. It surrounds the north and east sides of Lake Stevens, the largest and deepest lake in Snohomish County, with an area of and an average depth of . The lake has of shoreline and is fed by Lundeen Creek, Mitchell (Kokanee) Creek, and Stitch Creek. It drains into Catherine Creek, which then flows to the Pilchuck River. The lake's relatively small watershed, at , minimizes the effect of upstream pollution but reduces flow to remove pollutants. Lake Stevens installed aeration system in the 1990s to control the release of phosphorus from lake sediments, which caused unwanted algae growth. Most of the shoreline is heavily developed, with little remaining native vegetation, and Lake Stevens is used for recreational fishing, swimming, boating, and skiing.