These lowland sub-basins flank the Snohomish River Estuary and adjacent nearshore areas and have the highest levels of current land development and future development pressure in the basin. Coho and chum salmon and cutthroat and rainbow trout use these waterbodies for spawning and rearing (Pentec Environmental and NW GIS, 1999). There is little to no Chinook spawning in these creeks and drainages, but the lower reaches provide, or potentially provide, rearing habitat for Chinook and other salmon spawning throughout the basin. Bull trout may also use the sub-basins as foraging habitat, although such use has not been documented.

Overall riparian forest conditions are substantially degraded, but pockets of maturing second-growth riparian forest can be found in deep ravines. Benthic sampling in most urban growth areas in this sub-basin strategy group, including sites within the Sunnyside and Allen Creek sub-basins, rated 'poor' on a benthic index of biotic integrity ranging from very poor to excellent. Quilceda Creek scored on the low end of the 'good' range (Snohomish County Drainage Needs Report, 2002).

The Allen Creek sub-basin has approximately 16 miles of fish-bearing streams and 15 miles of non-fish-bearing streams. Coho and chum salmon
and cutthroat trout are the predominant salmon species that spawn in Allen Creek and its tributaries. Spawner data indicate that salmon productivity in Allen Creek declined substantially between 1987 and 1993 (Snohomish County Drainage Needs Report, 2002). This sub-basin has been identified as having low dissolved oxygen, a high level of fecal coliform, lack of riparian habitat along the stream system, and local erosion problems.

The Quilceda Creek sub-basin has seven fish-bearing streams that total approximately 31 miles, and nearly 27 miles of non-fish-bearing streams.
Coho and chum salmon, cutthroat trout, and rainbow trout are the predominant salmon species that use the Quilceda Creek sub-basin. Healthy forested and emergent wetlands remain near the mouth of Quilceda and Sturgeon creeks. They provide critical rearing habitat for Chinook and bull trout, and also contain several tribal archeological sites and rare plants. Prior to settlement, extensive wetlands covered the valley floor in the vicinity of Marysville. Habitat problems identified include numerous blocking culverts, high levels of fine sediment, high levels of impervious surface, low dissolved oxygen levels, and loss of riparian forests and wetlands.

The Everett Coastal drainages sub-basin contains nine, small, second-order coastal streams. They have some use by coho salmon and cutthroat trout, and potentially chum salmon, but it is unlikely that they ever supported Chinook salmon given their small size. Headwater areas are heavily developed, but steep-walled ravines typical of these drainages have protected riparian zones. The Burlington Northern/Santa Fe Railroad line impacts creek deltas and restricts access in some locations.