Blue hole
Sawmill Sink
A fossil-rich inland blue hole on Abaco with a toxic hydrogen sulfide layer and oxygen-free deep water. It is a research site: underwater activity is reported to need a special permit.
Sawmill Sink is a near-circular shaft about 15.5 m across in the pine forest of south-central Great Abaco. Below a fresh-water cap lies a cloudy, hydrogen sulfide-rich mixing layer that blocks daylight, and beneath that is salt water with no oxygen, which is why bones and plants on its rubble cone have survived for thousands of years.
The site is known through scientific diving rather than tourism. Fossil recovery there produced extinct tortoises, dozens of Cuban crocodiles, birds, bats and human remains, studied by a team of Bahamian and US researchers. Because of these finds, published accounts report that any underwater activity requires a special permit, and the sink is inside the South Abaco Blue Holes Conservation Area.
The environment
Fresh water to about 9.5 m, a hydrogen sulfide-bearing halocline to about 27 m, and anoxic salt water below; a talus cone from about 9 m to 34 m; cave passage continuing south to 54 m.
Conditions
The hydrogen sulfide layer blocks light and is poisonous; National Geographic reported a bacterial layer colouring the water at roughly 9 to 11 m.
Typical ranges from published sources, not current conditions.
Every fact on this page, with its source (7)
| Fact | Status | Source |
|---|---|---|
| The opening is nearly circular and up to 15.5 m in diameter. | Verified | [1] |
| Fresh water extends to 9.5 m, a hydrogen sulfide-bearing halocline and mixed zone to 27 m, and anoxic salt water below; a talus cone lies from 9 to 34 m. | Verified | [1] |
| The cave associated with the sink extends more than 600 m south to depths of 54 m.As published in 2007. | Verified | [1] |
| Bacteria colour the water at about 30 to 36 ft (9 to 11 m), and poisonous hydrogen sulfide is present in that layer and the one below.2010 magazine account. | Reported | [3] |
| Any underwater activity at Sawmill Sink requires a special permit because of archaeological discoveries.2019 report; authority not named. | Reported | [2] |
| A special permit is required for any underwater activity.2019 report. | Reported | [2] |
| The sink is in the pinelands of south-central Great Abaco Island.Numeric coordinates withheld: permit-only research site. | Verified | [1] |
Verified: stated by an official or primary source we opened. Reported: from a secondary source only. Sources conflict: the note gives both versions. May be out of date: the newest source we found is old.
Written in our own words from the sources above. Report a correction