Fish Ladder

Salmon have always been vital to the Pacific Northwest’s ecosystem. The U.S. Army Corps of Engineers, Seattle District Engineer Maj. Hiram M. Chittenden, for whom the locks are now named, understood this and planned on incorporating a fish ladder in the designs when he proposed building them in the early 1900s.

All fish, including endangered salmon, must pass through the locks, spillway or the fish ladder to move between Lake Washington and Puget Sound. In 1976, Corps of Engineers officials renovated and improved the ladder to reflect changes in fish conservation. Today's ladder has 21 steps, or weirs, which allow the fish to swim upstream on a gradual incline. For many years the locks has been the focus of studies detailing migrating juvenile and adult salmon behavior.

A cooperative effort among the U.S. Fish and Wildlife Service, Washington State Department of Fish and Wildlife, Muckleshoot Indian Tribe, City of Seattle, King County and Water Resource Inventory Area 8 and U.S. Army Corps of Engineers Seattle District, the studies have resulted in many fish passage improvements.

Salmon and steelhead hatch and partially grow up in rivers and streams. They then journey to the sea, spending most of their adult lives. Near the end of their life cycle, the few surviving salmon journey back to spawn in the streams where they were hatched years before. Between hatching and spawning, the returning fish must survive many hazards. In the end, less than one egg in 1,000 survives to spawn as an adult.

When we see them at the Locks they are silver color, called 'ocean phase,' and are easily identified from other salmon species by the lack of spots on their backs.  Sockeye will average 6-8 pounds and 24-30 inches long.  As they journey through fresh water to the spawning beds their bodies will take on the distinctive red color called 'freshwater phase.'

Moving through the Canal and lakes they will reach the spawning beds in late September/early October.  Each female will lay several thousand eggs in the gravel of the riverbed where they remain for three months until hatching into tiny fish called alevins.  Both male and female salmon die after spawning, thereby becoming an important part of the ecosystem as their decaying bodies return essential nutrients - nitrogen and phosphorus - to the soils along the streams.

The best times for viewing salmon migrating upstream in the ladder are:

  • Chinook, or King Salmon, July through November (best viewing last two weeks of August)
  • Coho, or Silver Salmon, August through November (best viewing last two weeks of September)
  • Sockeye, or Red Salmon, June through October (best viewing July)