Lake Sammamish covers about 7.6 mi2 (19.8 km2), with a length of 8 mi (13 km) (north-south) long and a width of 1.2 mi (2 km), and drains an area of 260.5 mi2 (250 km2). The mean depth of the lake is 58 ft (17.7 m) and a maximum of 105 ft (32 m). Issaquah Creek is the major tributary to Lake Sammamish, with other inflow from creeks such as Tibbets, Lewis and Laughing Jacobs. The Sammamish River drains the lake at the north end and a flow control weir in Marymoor Park controls the lake discharge. The majority of the lake shoreline is privately owned, mostly for residential uses. There are a few major parks along the lake shoreline, including Marymoor Park at the north end, Idylwood Park on the northwest side, and Sammamish State Park at the south end, which includes the mouth of Issaquah Creek. As with Lake Washington, much of the shoreline of the lake is armored and many docks and piers have been constructed to support recreation. Lake Sammamish is used as a migration corridor by the Issaquah Creek population.

There is similarity in habitat conditions and habitat use by Chinook between Lake Washington and Lake Sammamish. The shoreline habitat conditions of Lake Sammamish are important for juvenile Chinook (Tabor and Piaskowsi 2002; Tabor et al. 2003) coming from the Issaquah Creek system. Shoreline armoring affects the quality and quantity of riparian vegetation and woody debris. Overwater structures affect both prey resources and migration behavior of Chinook salmon. These alterations have reduced the amount and quality of shallow water habitat.

Juvenile Chinook in the Issaquah system out-migrate through Lake Sammamish and the Sammamish River to Lake Washington, the Ship Canal, and the WRIA 8 nearshore. Restoration of each of these areas would benefit Chinook that spawn in the Issaquah subbasin, but the greatest restoration potential for Chinook spawning in the Issaquah sub-basin exists in Lake Sammamish, particularly in areas adjacent to the mouth of Issaquah Creek. Shoreline areas at the head of the Sammamish River in and around Marymoor Park have the next highest restoration potential within Lake Sammamish. Based on the EDT habitat modeling effort, it is hypothesized that juvenile migrants would benefit from actions that reduce predation and the efficiency of predator species such as cutthroat and residualized coho. The abundance and efficiency of predation appears to be driven primarily by conditions that limit cover for Chinook and increase exposure to predators, such as bank hardening, steep slopes, and a lack of LWD and shoreline vegetation.