Water is leaking from the ceiling of the SR 99 tunnel under downtown Seattle onto traffic in the southbound lanes.
The Washington State Department of Transportation (WSDOT) is investigating the leak, and said the tunnel is still safe to travel through.
The Seattle Fire Department noticed the leak and told WSDOT around 1 p.m. Friday.
The southbound lanes were already scheduled to close at 10 p.m. Friday for planned overnight maintenance. Crews said they will now use the opportunity to determine a cause and repair for the leak.
The tunnel opened to traffic on Feb. 4, 2019 after the closure of the Alaskan Way Viaduct.
The tunnel has a history of issues, dating back to its construction.
More than a decade ago, the $2.8 billion funding plan for the tunnel was approved. Bertha, the world's largest tunneling machine, was brought in to make it happen. That machine overheated and needed repairs, leading to delays. It took about six years to finish the tunnel.
On average, 57,000 people travel through the tunnel each day.