The spooky, underwater forests of Lake Washington and Lake Sammamish | KUOW News and Information

The spooky, underwater forests of Lake Washington and Lake Sammamish

May 11, 2017

At the southern end of Lake Sammamish, just off Greenwood Point, several jagged, gray logs stick up from the water. They’re the only visible sign of an ancient, perfectly-preserved underwater forest that’s been sitting at the bottom of the lake for over a thousand years.

KUOW Local Wonder listener Scott McGee wanted to know more.

Warning: The story is a little scary. It starts with a massive earthquake that rattled the region around a thousand years ago — an earthquake so violent that some expanses of land were pushed 20 feet in the air and massive landslides occurred.

The underwater forest in Lake Sammamish exists because of one of those slides. Huge chunks of earth broke away from the lake’s shores and slid into the water, trees and all, and that’s where they’ve been since.

“They slid down with such a deep amount of dirt that they slid standing up into the water,” said Michal Rechner, with the aquatics division at the Washington State Department of Natural Resources. “It’s really quite simple when you think about it.”

But ... we still had questions.

Just how big was this earthquake?

Big. Like, really, really big.

Big enough that the sunken forests in Lake Sammamish aren’t the only ones. There are three groups of underwater trees in Lake Washington (one just north of Kirkland and two off the coast of Mercer Island).

Big enough that Bill Steele of the Pacific Northwest Seismic Network told us in 2015: "That earthquake, if it reoccurred today, it would really impact the city, probably the worst seismic disaster in the country.”

Big enough that when evidence of the massive earthquake emerged in 1992, the Seattle Times described it like this: “The quake caused rock avalanches in the Olympics, uplifted southeastern Bainbridge Island 20 feet and Alki Point 13 feet, produced a tsunami that hit the southern tip of Whidbey Island, drowned West Point with a monster wave, and sent trees sliding 200 to 400 yards into Lake Washington.”

Survey map of Lake Washington with the area with the underwater forest circled.
Credit Courtesy of Ben Griner of Coastal Sensing & Survey

Researchers pieced the story together using radiocarbon dating from the submerged trees, along with an elaborate puzzle of other clues. They discovered the earthquake likely happened along what’s now called the Seattle Fault, which runs from Bainbridge Island to Lake Sammamish — a rarity among faults because it runs east to west instead of north to south. (In case you’re wondering, it cuts through Seattle somewhere around Safeco Field.)

What’s it like in an underwater forest?

Wet.

But seriously, it’s spooky. This video taken among the trees off the southern coast of Mercer Island might give you “Blair Witch Project” flashbacks.

Local diver Ben Griner has explored the sunken forests of Lake Washington — with sonar technology and in underwater diving excursions. He describes the drowned trees off the southern coast of Mercer Island as a thrill to swim through (although he gets not everyone would see it that way).

“It’s certainly a disorienting dive,” he said. “A lot of people call it really freaky. Other people describe it as exciting and interesting.”

The lake is pitch black at that depth — and being underwater can mess with one’s sense of movement. Griner said it’s sometimes difficult to tell if the water is moving or he is, and divers often bump into things.

“Because of how long the forest has been under water and how busy the lake is, most trees are just the trunks now,” he said. “It can be a little creepy, but it’s really fun to swim through the trees.”

After a thousand years underwater, the trees are well preserved due to low oxygen levels. And submerged tree sap is eventually replaced with minerals that make the wood extremely hard and valuable. Furniture made from logs salvaged from lakes sells for thousands of dollars. (If you’re in the market for pricey underwater furniture, check out this armoire from West Elm that’s going for $2,500 or this coffee table priced at $3,500.)

OK, so why hasn’t anyone made furniture out of these trees yet?

The trees belong to the state — under the jurisdiction of the Department of Natural Resources — so anyone who wants to salvage them would have to pay fair market value. That, coupled with the cost of hauling the trees to the surface and moving them elsewhere, makes salvaging less appealing to potential buyers.

“I probably field one or two phone calls a year from someone interested in salvaging the logs,” Rechner said. He said interest fades when the caller looks into the economics and logistics.

In 1995, a Kirkland businessman was convicted of timber piracy for removing logs from the sunken forest in Lake Washington near Kirkland. And in 2005, an unsuccessful bill in Olympia outlined a plan to salvage trees to raise money for the Burke Museum at the University of Washington.

For now, at least, the underwater forests will remain at the bottom of their lakes — and that’s fine with the folks over at Natural Resources. After a thousand years, the underwater forests have become a habitat for animals and organisms in the lake.

“We’re not really all that interested in seeing them removed,” Rechner said.

And the trees aren’t alone down there. Beneath the surface in Lake Washington, there are also planes, trains and about 400 downed boats.