(CNN) -- A massive dock, possibly debris from the March 2011 tsunami that struck Japan, has washed ashore in Washington state's Olympic National Park.
A U.S. Coast Guard helicopter spotted the dock Tuesday along a remote section of the park's coast, the Washington State Marine Debris Task Force said.
Authorities were trying to reach the dock by ground Wednesday to determine whether it was tsunami debris and whether it harbors invasive species that could harm the area.
The National Park Service has closed the beach in the area to the public.
The Coast Guard had been searching for the dock since Friday, when a fishing vessel spotted it adrift in the ocean.
Washington Gov. Christine Gregoire thanked the Coast Guard for finding the dock.
"They were out in challenging conditions looking for a needle in a haystack, and they found it," she said in a statement.
If the dock is confirmed as tsunami debris, it would be the second to wash ashore in the Pacific Northwest this year.
In June, a 66-foot-long dock turned up near Agate Beach, Oregon.
In September, a 50-foot-long dock was spotted off the Hawaiian islands of Maui and Molokai.
Alaska has seen much debris from the tsunami wash up on its beaches this year.