12 Interesting Facts About Lake Union, Washington’s Vibrant 580 Acre Freshwater Lake

Welcome to Lake Union

Lake Union sits in the middle of Seattle, connecting Puget Sound to Lake Washington. Native American tribes were the first to use these waters, mainly for fishing and travel.

Today, people boat and play in the waters, vessels travel through it, and hundreds of floating homes sit on its surface. Here’s why you should visit this busy waterfront.

Glaciers Created Lake Union

A huge ice sheet called the Vashon Glacier carved out Lake Union about 12,000 years ago. This glacier was more than 3,000 feet thick and shaped the lake basin as it moved south.

When the ice melted, it left a deep hole that filled with water from rain and melting ice. Some parts of the lake are 49 feet deep because of how the glacier dug into the ground.

The same glacier created Capitol Hill and Queen Anne Hill rising 456 feet high with great views.

The First Gas Plant on the West Coast

Gas Works Park (one of the first large-scale coal gasification plants) used to be the Seattle Gas Light Company’s plant from 1906 to 1956. Instead of tearing down the old factory, the city turned it into a park in 1975.

They kept the old towers and machines as part of the park’s design, which was a new idea at the time. The soil was full of chemicals from the factory, so they used helpful bacteria to clean it up.

This method of cleaning dirty soil was one of the first of its kind.

Seattle’s Floating Home Community

Lake Union has over 500 floating homes, making it the largest community of its kind on the West Coast. These aren’t just houseboats – they’re real homes that connect to the city’s water pipes and sewers, with some built as far back as 1907.

The first floating homes were simple cabins built by lumber workers on log rafts. The city has strict rules about these homes to protect the lake. Each home must be built in a way that won’t harm the water or wildlife.

Lake Union’s Role in World War II Aviation

The place was an important testing site for Boeing’s seaplanes during World War II. Boeing utilized Lake Union for various aircraft tests, including the B-29 Superfortress and other military aircraft.

The first flight of the Boeing B-1, a significant model, took place from Lake Union in 1919. The lake is still used for seaplanes today, with about 50,000 takeoffs and landings happening each year.

Why Lake Union Never Freezes

Even when Seattle’s temperature drops to 20°F (-6°C), Lake Union stays liquid. Several things keep it from freezing: it’s average 34 feet depth, the city buildings heat, and the boats that keep the water moving.

The deepest parts of the lake stay around 45°F (7°C) all year. Because the lake doesn’t freeze, over 100 water-based businesses (marinas, seaplane operations, and recreational boating activities) can work year-round.

Ancient Fishing Ground of the Duwamish People

The Duwamish tribe and other Coast Salish peoples fished in Lake Union for more than 5,000 years. They primarily caught Chinook, coho, steelhead, and chum using special nets and underwater fences called weirs.

They also used plants from the shore, making baskets from cattail reeds and canoes from cedar trees. Scientists have found fishing tools and sacred items from 3000 BCE near the shore, showing how long people have lived here.

Natural Springs Under Lake Union

Lake Union is fed by natural springs and historically drained into Salmon Bay. Licton Springs, located in North Seattle, is a notable natural spring that historically flowed southward to Green Lake.

Before the Lake Washington Ship Canal was built in 1916, these springs helped keep the lake’s water level steady. During quiet times on the lake, you can sometimes see where the springs bubble up to the surface, especially near the east shore.

Ship Traffic Through Lake Union

Approximately 800,000 people pass through the locks each year, along with thousands of vessels. The Hiram M. Chittenden Locks, which connect Lake Union to Puget Sound, accommodate nearly 50,000 boats locking through each year.

Boats of all sizes use Lake Union, from small kayaks to 100-foot ships. The Arthur Foss, a historic tugboat built in 1889, is preserved at the Lake Union Dry Dock, which is located along the eastern shore of the lake.

Wildlife in an Urban Lake

Despite being in the middle of the city, Lake Union is home to 15 kinds of fish (migratory route for salmon and steelhead trout) and more than 30 types of water birds (blue herons, bald eagles, and kingfishers).

The docks and floating homes create places for mussels while Harbor seals occasionally enter Lake Union to forage. People work to keep the lake clean and healthy for these animals by checking the water quality and fixing damaged areas around the shore.

Special Weather Patterns

Lake Union often has thick fog, especially on autumn and winter mornings. This happens when cold air meets the warmer lake water, which stays about (43°F to 46°F).

The fog can get so thick that you can’t see more than 100 feet ahead. The hills and buildings around the lake shape how the fog moves and flows. These fog banks usually appear early in the morning and clear up by midday.

Seattle’s First Airport Was on Water

Lake Union was Seattle’s first airport, starting in 1916.

It wasn’t a regular airport – seaplanes landed on the water instead of runways. The lake’s first international flight took off in 1920. The calm water and central location make it perfect for seaplanes.

Kenmore Air Harbor Seaplane Base reported 43,500 aircraft operations in the 12 months ending December 31, 2022, averaging 119 operations per day. ​

Scientific Studies of Lake Union

Scientists from major institutions like the Washington Department of Ecology focus on aspects such as algae growth and invasive plant species.

The Pacific Northwest National Laboratory’s Seattle campus is situated here, often examining contaminants like microplastics, heavy metals, and nutrient loading from nearby development.

King County also plays a role by monitoring swimming beaches on Lake Washington and Lake Union for toxic microbial growth.