The Outer Basin (also referred to as the Outer Harbour) serves as the entry point for vessels approaching Cardiff Bay before locking through the barrage into the bay itself.

Boats arriving via the Wrach Channel should contact Barrage Control on VHF Channel 18 before entering, and permission must be obtained prior to entry. An initial call is recommended when in the vicinity of the Outer Wrach Cardinal Buoy.

The barrage locks operate year-round on a 24-hour basis, with access dependent on draught, remaining viable on all but the lowest spring tides. Outbound locks run on the hour and half-hour.

Vessels approaching by night follow a buoyed channel guided by sector lights into the Outer Harbour.