How big are the two Ballard Locks chambers?

The large lock is 80 by 825 feet with an intermediate gate so mid-size traffic doesn't cycle the whole chamber; the small lock is 30 by 150 feet and handles most recreational traffic. Source: US Army Corps of Engineers.

How much does the water level change in the Ballard Locks?

The lakes are held at 20–22 feet above sea level while Puget Sound rises and falls with the tide, so the lift is typically around 20 feet — as much as 26 feet at an extreme low tide, as little as ~6 feet at a very high one.

Does the tide change how long a lockage takes?

Measurably, almost not at all. Joining 1,173 lockage records to NOAA's Seattle tide gauge and controlling for time of day: about 0.07 minutes of chamber time per foot of tide. Gates, valves and boat loading dominate the cycle, not the water height.

Why do the Ballard Locks exist?

Three official jobs: hold Lake Washington and Lake Union at 20–22 feet above sea level, keep Puget Sound saltwater out of the fresh lakes, and move boats between the two levels. They opened July 4, 1917.

Are the Ballard Locks really the busiest in the country?

By vessel count, yes — the Corps itself calls them the nation's busiest at roughly 45,000 vessels a year, most of them recreational. By tonnage they are tiny compared to Mississippi River locks.

How the Ballard Locks actually work

Last updated 2026-08-29 · facts from USACE Seattle District; measured timings from LockPush data

The Hiram M. Chittenden Locks connect saltwater Puget Sound to the freshwater Lake Washington Ship Canal. Designed by Major Hiram M. Chittenden, first vessel through August 3, 1916, formally opened July 4, 1917 — 63 years to the day after the canal was first proposed at an 1854 picnic. On the National Register of Historic Places since 1978, and by vessel count the busiest lock complex in the United States: ~45,000 vessels a year, two-thirds of them pleasure craft, plus well over a million visitors.

Two chambers, three jobs

	Large lock	Small lock
Size	80 × 825 ft (intermediate gates)	30 × 150 ft
Walls	Fixed — crews tend lines	Floating — tie and ride
Typical use	Barge tows, big vessels, overflow	Nearly all recreational traffic
Measured chamber time	~29 min median	~17 min median

The Corps' three official purposes: hold the lakes at 20–22 ft above sea level, block saltwater intrusion, and move boats across the difference. In normal operation the small lock does almost all the work — LockPush's chamber inference puts only ~9% of lockages in the large chamber.

The lift, and why tide barely matters to your wait

Because the lakes are fixed and the Sound tides, the lift varies from ~6 ft (extreme high tide) to 26 ft (extreme low). Intuition says high tide = shorter cycle. Measurement says otherwise: joining 1,173 lockages to NOAA's Seattle gauge, tide height moves chamber time by ~0.07 minutes per foot — a couple of minutes across the entire tidal range. Filling isn't the bottleneck; gates, valves and loading boats are.

Saltwater defense and salmon

A hinged saltwater barrier on the large lock floor blocks the dense salt wedge; deep-draft vessels (over 14 ft) signal one long, two short blasts to have it lowered. A drain system returns ~160 cfs of salt water downstream, mostly reused to supply the fish ladder.
The fish ladder (1916, rebuilt 1976 to 21 weirs) carries salmon past the dam — one of the few ladders anywhere at a salt/fresh boundary, with a public underwater viewing gallery. Sockeye peak in July, Chinook late August, coho late September.
Six spillway tainter gates (32 × 12 ft each) manage lake level to a hundredth of a foot; in spring, smolt flumes shoot young salmon safely past the dam.

What this means for your transit

Everything above is the mechanism behind the numbers on the wait-times page: an ~18-minute mechanical chamber cycle that nothing beats (no boat under 10 minutes in 30 days of records), a queue driven by demand and commercial priority, and a small lock that is the real server for recreational Seattle.

Common questions

How big are the two Ballard Locks chambers?: The large lock is 80 by 825 feet with an intermediate gate so mid-size traffic doesn't cycle the whole chamber; the small lock is 30 by 150 feet and handles most recreational traffic. Source: US Army Corps of Engineers.
How much does the water level change in the Ballard Locks?: The lakes are held at 20–22 feet above sea level while Puget Sound rises and falls with the tide, so the lift is typically around 20 feet — as much as 26 feet at an extreme low tide, as little as ~6 feet at a very high one.
Does the tide change how long a lockage takes?: Measurably, almost not at all. Joining 1,173 lockage records to NOAA's Seattle tide gauge and controlling for time of day: about 0.07 minutes of chamber time per foot of tide. Gates, valves and boat loading dominate the cycle, not the water height.
Why do the Ballard Locks exist?: Three official jobs: hold Lake Washington and Lake Union at 20–22 feet above sea level, keep Puget Sound saltwater out of the fresh lakes, and move boats between the two levels. They opened July 4, 1917.
Are the Ballard Locks really the busiest in the country?: By vessel count, yes — the Corps itself calls them the nation's busiest at roughly 45,000 vessels a year, most of them recreational. By tonnage they are tiny compared to Mississippi River locks.