On the Lake Washington Ship Canal, the Locks (at Ballard) prevent fresh and salt water from mixing.
Seattle’s Ship Canal crosses the city like a waistline, joining the freshwater Lake Washington to the waters of Puget Sound and the Pacific Ocean beyond.
The building of the Ship Canal in 1911-1917 was one of the biggest events in the history and development of Seattle, creating economic opportunities and advantages for maritime and for industries of all kinds.
The 2016-2017 centennial year of the Lake Washington Ship Canal and the Hiram M. Chittenden Locks (Ballard Locks) is being celebrated with a wonderful series of events and historic research projects.
The ship canal centennial project, called Making the Cut 100, will consider the impacts of the construction of the Locks, the Ship Canal, and the lowering of Lake Washington. The Making the Cut introduction to the history of the Ship Canal says,
The Fremont Bridge opening on the official celebration day of the Ship Canal on July 4, 1917.
“On July 4, 1917, Seattle’s local papers heralded the grand opening of the Lake Washington Ship Canal. A carnival and fireworks attracted 50,000 celebrants.
The canal connecting Puget Sound with the freshwater Lake Union and Lake Washington had been a long time coming. The history of the canal involves dreamers and schemers who combined self-promotion, subterfuge, and politics to achieve their goals. Contending forces ranged from one man with a shovel to the United States Navy, who initially desired a safe place to dock their ships, to local citizens, who stood to benefit financially from the canal. Despite their differences, they all shared a common belief that nothing less was at stake than the future direction of Seattle.”
Wedgwood in Seattle History 
Thanks for bringing this to our attention. Speaking of Seattle waterways, I also like the story of the dredging of Ross Creek as told by David B Williams, in Too High, Too Steep.
On page 111 of Too High and Too Steep, author David B. Williams mentions preliminary canal work which was done by hiring Chinese laborers. This was in the 1880s after a ship canal investment group was formed, which included city leader Thomas Burke who was also the instigator of the Seattle, Lake Shore & Eastern railroad (today’s Burke-Gilman Trail which runs along the present Ship Canal.) The Chinese laborers were directed to widen Ross Creek, just west of today’s Fremont, where logs were being floated out towards Ballard and then to Puget Sound to be loaded on ships. As I noted in my essay on this blog about John Ross, the Ross Creek work was not done until after he died in 1886 because he had interfered with it. Then a small spillway was built to hold back the waters of Lake Union until released so that the flow would help wash logs westward toward Ballard.
Thanks again for the pointer to Too High, Too Steep. Great read. Fundamentally changed the way I see Seattle and has sparked my interest in how the landscape of the city of Chicago has been changed by geology, the fire and the people. Thank-you!