The Great Abaco interior is riddled with blue holes — vertical shafts in the limestone bedrock that drop into flooded cave systems connected to the sea. They are among the most dramatic natural features of the Abacos and almost completely unknown to the average visitor.
Sawmill Sink, in the pine forest near Crossing Rocks, is accessible by a short walk through the trees and has been the subject of serious scientific study: the anaerobic deep water preserved bones of extinct tortoise, crocodile, and birds for thousands of years, giving researchers a window into the pre-human Bahamas. Diving or even wading in blue holes requires care — the deep water transitions abruptly from fresh to salt in a halocline layer that can disorient swimmers. Guided tours run from Marsh Harbour for those who want to see the blue holes safely.