Police spokeswoman Renee Witt says witnesses called police after watching two men set up a large wooden box with two red push-buttons, then leave. When one of the men came back to do more work on the project, he encountered a full-scale bomb scare, CBS Seattle reported.
Officers blocked off streets and called arson and bomb squad detectives to the Aurora Bridge. Boaters on nearby Lake Union were advised to stay well offshore.
Witt says the man told police the box was an art project for a graduate course at the University of Washington. Police determined the box was harmless and the man departed, taking his art project with him.
Witt says the man apparently had not considered that putting a big box under a bridge might scare some people.