The pier was found on a beach near Forks, a northwestern town in Washington, by the US Coast Guard, authorities said, adding the area is designated as a national park.
The local officials said they plan to check whether there are any invasive alien species attached to the pier before removing the debris from the water, Kyodo news agency reported.
The coast guard was searching for the pier after local fishermen reported an object drifting in waters off the state coast, as it could create a navigational hazard to vessels in the area.
In June, another floating pier swept away from the tsunami-stricken city of Misawa in Aomori Prefecture, was found washed ashore on a beach in the state of Oregon on the Pacific Ocean.