The below text is directly from the United States Coast Guard Sector Puget Sound:
The Coast Guard is planning to establish a 500 yard temporary security zone in the navigable waters of Elliott Bay, Seattle, WA within the Sector Puget Sound Captain of the Port (COTP) Zone. The security zone is necessary to ensure the security of the USCGC MUNRO during the commissioning ceremony at Pier 91.
This rule establishes a security zone from 6 a.m. though 6 p.m. on April 1, 2017. The security zone will cover all navigable waters within 500 yards of USCGC MUNRO at Pier 91 in Seattle, WA. The duration of the zone is intended to protect personnel, vessels, and the marine environment in these navigable waters while the commissioning ceremony takes place. During the enforcement period no person or vessel may enter or remain in the security zone without the permission of the COTP, Puget Sound or his Designated Representative. The COTP will grant general permission to enter the outer 400 yards of the security zone as long as those vessels within the outer 400 yards of the security zone operate at the minimum speed necessary to maintain course.
All vessel operators who desire to enter the inner 100 yards of the security zone or transit the outer 400 yards must obtain permission from the Captain of the Port, Puget Sound or a Designated Representative by contacting the Joint Harbor Operations Center at (206) 217-6001 or the on-scene patrol craft on VHF Ch 16.
If you have questions on this rule, call or email Petty Officer Zachary Spence, Sector Puget Sound Waterways Management Branch, U.S. Coast Guard; telephone 206-217-6051, email SectorPugetSoundWWM@uscg.mil