The Sammamish River population spawns in the tributaries to northern Lake Washington, the Sammamish River, and Lake Sammamish between September and November. This includes Bear, Little Bear, North, Swamp and Kelsey creeks, as well as the Issaquah creek system and Lewis and Laughing Jacobs Creeks. This population also contains artificial spawning Chinook from the Issaquah hatchery. Similar to migration behavior seen in the Cedar River, juveniles migrate into Lake Sammamish, the Sammamish River or Lake Washington either as fry or fingerlings between February and June. Juveniles rear as they migrate towards Lake Washington and typically enter the lake at a larger size than their fry migrant counterparts from the Cedar River. While a small portion of the Sammamish River juveniles use nearshore areas in Lake Washington, most fish are believed to move into offshore areas quickly. Sammamish River Chinook smolts pass through the Ship Canal and Locks to reach Puget Sound during May, June and July (DeVries 2001; DeVries 2002). As with other Chinook smolts from WRIA 8, they rear in marine nearshore areas of Puget Sound before heading to the ocean.

As with the Cedar River population, the number of naturally spawning Chinook from the Sammamish River population has declined in number in recent years.