[5]: 7–8  The construction of the locks profoundly reshaped the topography of Seattle and the surrounding area, lowering the water level of Lake Washington and Lake Union by 8.8 feet (2.7 m), adding miles of new waterfront land, reversing the flow of rivers, and leaving piers in the eastern half of Salmon Bay high and dry.

[6] As early as 1854, there was discussion of building a navigable connection between Lake Washington and Puget Sound for the purpose of transporting logs, milled lumber, and fishing vessels.

Thirteen years later, the United States Navy endorsed a canal project, which included a plan for building a naval shipyard on Lake Washington.

[7] In June 1910, the US Congress gave its approval for the lock, on the condition that the rest of the canals along the route be paid for locally.

[8] The Cedar River was rerouted into Lake Washington to provide sufficient water flow for operating the Locks.

The rerouting of the rivers opened up huge lowland areas for development but significantly disrupted the Duwamish salmon runs.

[citation needed] To rectify this problem, salmon runs were reintroduced allowing the fish to migrate through the locks.

[7] To allow for the intended boat traffic, three bridges were removed along the ship canal route, at Latona Avenue, Fremont, Stone Way.

Salt water began to make its way upstream toward Lake Union, requiring a system of siphons and flushing mechanisms.

[2]: 5 Operated by the US Army Corps of Engineers,[11] the locks were formally opened on July 4, 1917,[12] although the first ship passed on August 3, 1916.

[1] Vessels passing from the freshwater Lakes Washington and Union to Puget Sound enter the lock chamber through the open upper gates (A in the accompanying diagram).

[2]: 8  Using the small lock when boat traffic is low conserves fresh water during summer, when the lakes receive less inflow.

Over 1 million tons of cargo, fuel, building materials, and seafood products pass through the locks each year.

[4]: 6 South of the small lock is a spillway dam with tainter gates used to regulate the freshwater levels of the ship canal and lakes.

This hollow metal barrier is filled with air to remain in the upright position, blocking the heavier salt water.

[2]: 3 The fish ladder at the Chittenden locks is unusual—materials published by the federal government say "unique"—in being located where salt and fresh water meet.

[10]: 2 Pacific salmon are anadromous; they hatch in lakes, rivers, and streams—or, nowadays fish hatcheries—migrate to sea, and only at the end of their life return to fresh water to spawn.

In order to provide enough water to operate the Locks, Cedar River was rerouted into Lake Washington (which was lowered 9 feet).

Cedar and White Rivers did support significant Salmon runs but also created severe flooding conditions for the early settlers.

In a few years, the surviving adults return, climb the fish ladder, and reach their spawning ground to continue the life cycle.