Lake Union got its name at Seattle's Fourth of July picnic in 1854. A settler named Thomas Mercer stood up and suggested calling it Lake Union, because he figured a canal would someday unite Lake Washington, this little lake and Puget Sound. He was right. It just took 63 years: the Ballard Locks were dedicated on July 4, 1917, 63 years to the day after that picnic.
Lake Union is a stop on my Inside Seattle Engineering tour. The whole canal system you see today started as one guy's idea at a picnic.
What it was called before
Before 1854, settlers knew it by its Chinook Jargon name, Tenas Chuck, or "little water." The big lake to the east had a few names going around, including Hyas Chuck, "big water." At the same picnic Mercer proposed calling that one Lake Washington. Mercer Island, out in the big lake, was later named after him too.
Why the canal took so long
In 1854 Lake Union was pretty cut off. A natural dam at Montlake blocked it from Lake Washington, and only a small stream drained it out toward Salmon Bay. A guy named Harvey Pike started digging a ditch between the lakes in 1860 and gave up.
For decades people argued about the best route. The Army Corps of Engineers backed a route through Lake Union in 1891, and construction on the Locks started in 1911. In 1916 they lowered Lake Washington almost nine feet to match Lake Union. The Locks were dedicated the next summer, and the whole canal was declared finished in 1934, 80 years after Mercer's picnic.
Where to see Mercer's canal today
The Ballard Locks. This is where the boats step down from the lakes to Puget Sound. The Locks hold the lakes at a steady level, between 20 and 22 feet on the Corps' gauge, and keep salt water out of them. More in my Ballard Locks guide.
The Fremont Cut and the Montlake Cut. The narrow stretches of the canal on either side of Lake Union, with drawbridges going up for boats. Here's why Seattle's drawbridges open.
Gas Works Park. On the north shore, with one of the best looks across the lake at downtown. Lots of boat traffic, seaplanes, and sometimes a pirate ship full of kids with water cannons.
Quick answers
Who named Lake Union? Thomas Mercer, an early Seattle settler, at the Fourth of July picnic in 1854.
Why "Union"? He expected a canal to connect, or unite, Lake Washington and Puget Sound through this lake.
When did the canal open? The Locks were dedicated July 4, 1917. The canal was declared complete in 1934.
See it with me
On my private Inside Seattle Engineering tour we stop at Gas Works Park on Lake Union and the Ballard Locks, then cross the I-90 floating bridge. If you'd rather do the classic city highlights, the 3-hour Seattle City Tour also stops at the Locks and drives through South Lake Union.
More on how Seattle works: Why Seattle might be the most engineered city in America
