The Snohomish River Estuary is the second largest in Puget Sound and includes the Snohomish River mainstem, three distributary sloughs (Ebey, Steamboat, and Union), and marshes between Possession Sound and the divergence of Ebey Slough from the mainstem. The estuary, a highly productive and diverse environment, provides unique and critical habitat for Chinook and other salmon for rearing, migration, and transitioning between fresh- and saltwater (smoltification). Bull trout overwinter and forage in the estuary as well. Tidal circulation drives hydrologic processes in the estuary sub-basin. Vegetation, elevation, and salinity vary across the estuarine landscape. The quantity of estuarine tidal habitat, which is critical for juvenile salmon, has been severely diminished.

Three estuarine zones have been delineated based on habitat characteristics. The emergent marsh, located at the mouth of the delta, has the highest level of primary production, salinity, and density of blind tidal channels. Farther upstream, as elevation increases and salinity decreases, open marshes give way to scrub shrub vegetation and forested wetlands. A productive brackish (mixed salt- and freshwater) marsh fringe typically lies between the river channel and mud banks and adjacent scrub-shrub or forested habitats. Each
zone in this complex ecosystem provides unique functions to Chinook and other salmon species.

The estuary was settled and logged in the late 1800s and early 1900s. Diking began in the 1860s and reached its maximum extent in the 1950s. Levees that have disconnected the Snohomish River from tidelands and marshes have dramatically altered the hydrology of the estuary, resulting in loss of tidal channels and marsh. Recent natural and intentional actions have restored several hundred acres of these habitats (City of Everett and Pentec, 2001). Extensive diking in conjunction with riparian clearing and wood removal has also reduced habitat complexity in the margins of distributary sloughs and the mainstem (Snohomish Basin Salmon Recovery Forum, 2001). Other habitat problems in the estuary include tide-gates that restrict fish access to tributary creeks, altered sediment deposition patterns, and degraded water quality. Degraded water quality can be seen in late summer with high temperatures and high fecal coliform counts that do not meet State of Washington water quality standards. The U.S. Army Corps of Engineers performs dredging operations in the estuary every few years in the lower four miles of the Snohomish River.

How can this sub-basin strategy group best contribute to recovery'

Loss of 85% of the historic tidal marsh area, reduced edge habitat complexity along major slough channels, and habitat fragmentation have depressed salmon population performance. Addressing these problems will provide significant improvements in abundance, productivity, and diversity for Chinook, bull trout, and other species.