Lyon Creek originates from wetlands in south Snohomish County and flows 3.8 miles through Lake Forest Park, before draining into the northwest corner of Lake Washington. The drainage basin is approximately 2,600 acres in size, one of the smallest of the Lake Washington tributary systems. The upper drainage basin is composed of a westerly fork within the City of Mountlake Terrace and an easterly fork in the City of Brier. The west fork of Lyon Creek traverses three wetlands within the City limits of Mountlake Terrace. Two of the three wetlands are on City park property. Lake Forest Park recently purchased the third wetland area that is now City park property that drains into a tributary of Lyon Creek just north of Ballinger Way at 195th Steet (Kerwin 2002). The creek is placed in Ecology’s Noncore Salmon/Trout Aquatic Use Category which sets criterion for the protection of spawning, core rearing, and migration of salmon and trout, and other associated aquatic life.
Land use in the basin is roughly fifty percent residential and fifty percent commercial (PSCOG, 1981). Much of the watershed was developed in the late 1970’s (Kerwin 2002). During the conversion in land use virtually no stormwater retention/detention facilities were constructed to mitigate the effects of greater basin wide total impervious area on the stream system. Peak flows increased from an average of 0.5 cfs in the early 1970’s to 30 cfs in the late 1970’s. A 1981 Comprehensive Drainage Plan (Entranco, 1981) was prepared to address downstream flooding that resulted from the much-altered hydrology.
Salmonid habitat suitability of Lyon Creek has been impacted by high storm flows that have resulted in degraded substrate and lack of spawning habitat. Historically, sockeye and coho salmon and cutthroat and rainbow trout had been observed throughout Lyon Creek.
Since 2000, volunteers with the Salmon Watcher Program have been watching for salmon at River Mile (RM) 0.1 in Lyon Creek. Sockeye and coho salmon have been observed in the creek.