Port of Oakland FREE Harbor Tours 2015 -- The Port of Oakland is pleased to offer free harbor tours from June through October 2015 on the historic U.S.S. Potomac located at 540 Water Street (at Clay Street) in Jack London Square, Oakland 94607. The tours will be held monthly and the tour will last approximately 90-minutes. Registration will open on the first Monday of each month at 10 a.m. (PDT) and will remain open until filled. Registration is on a first come, first served basis.