STEILACOOM, Wash. -- A device that looked like a bomb but was actually a homemade toy submarine prompted authorities to close the Steilacoom ferry dock for more than four hours.

The device involved some plastic pipes taped together. It was spotted jammed under a walkway leading to the dock Thursday at about 1:45 p.m.

Pierce County sheriff's spokesman Ed Troyer said police used a remote-controlled robot to examine the item and determined shortly after 6 p.m. that it was not explosive.

Troyer said nearby children apparently made the toy submarine and lost it in the water. One of the children's mothers brought her son down to the dock and he told investigators what had happened.

Troyer said the toy apparently floated to the ferry dock and became stuck under the walkway.

Ferry and nearby railroad traffic was disrupted while the device was examined.

Burlington Northern Santa Fe spokesman Gus Melonas says eight trains were held back as a precaution.

Among the many people affected by the shutdown ferries were more than 200 workers at the Special Commitment Center for sex offenders on McNeil Island. They were stranded there after their shifts ended, according to Ron Van Boening, the center's chief administrator.