The outer barrier reefs north of the ribbon reefs are composed of two distinctly different reef types, here called 'deltaic' reefs and far northern 'dissected' reefs. Two reefs of each of these types are described. The deltaic reef system is composed of 96 km of reef front characterized by the presence of regular, well defined channels containing very strong tidal currents, and also by the presence of a deltaic pattern at the reef back. The dissected reefs are the northernmost of the barrier reefs. They are composed of many small E-W elongate reefs interspersed by many wide channels. Both reef types are part of the one structure, their differing surface morphologies being attributed to bathymetric and hydrodynamic factors of the present and of the past.