Hidden in plain sight: Robots reveal ‘shipwreck city’ below the surface of a Washington lake

WASHINGTON — Hidden beneath the surface of Lake Union in Washington state, dozens of long-forgotten shipwrecks are being rediscovered using modern robotics — offering a rare glimpse into underwater history in places too polluted or dangerous for divers.

A high-resolution sonar survey has identified nearly 100 “targets” on the lakebed, including barges, work boats and other debris. Experts estimate roughly half of those could be shipwrecks, though the exact number is unconfirmed.

Ocean engineer and remotely operated vehicle (ROV) specialist Phil Parisi has begun documenting the wrecks, using robotics to capture detailed images in conditions where human divers face safety risks.

“We need to document what these wrecks look like today,” Parisi said.

So far, he has explored seven sites, including some not previously identified in sonar mapping. The technology allows for longer exploration times and clearer imaging in low-visibility waters.

“It’s shocking how much is down there,” Parisi said. “It’s shipwreck city.”

Many of the vessels are believed to have been intentionally sunk after salvageable parts were removed, a practice historically used to avoid costly disposal. As a result, the sites often lack valuable artifacts but remain important for understanding maritime and industrial history.

Rather than treasures, Parisi said he frequently encounters modern debris such as tires and plastic waste at nearly every location.

“It’s kind of a ghost town down there,” he said, noting that plant life drops off beyond about 25 feet due to lack of light, leaving much of the lakebed barren.

Historians say efforts like Parisi’s are helping close gaps between sonar data and visual documentation, using non-invasive methods to study underwater sites that have largely gone unexplored.

Nathaniel Howe of the Puget Sound Maritime Historical Society said robotic exploration offers a safer, more responsible way to study submerged history compared to traditional salvage efforts.

Advancements in sonar and robotic technology have played a key role in other major discoveries, he noted, and could continue to reshape how underwater archaeology is conducted.

For now, researchers say exploration of the lake’s hidden shipwrecks is only beginning — revealing a largely unseen world beneath the surface.