Andros Island is the largest island of the Bahamas and North Andros is the sixth largest island in the West Indies at roughly 6,000 km2 (2,300 sq mi) in area and 167 km (104 mi) long and 64 km (40 mi) wide at its widest point. It is actually composed of three major islands: North Andros, Mangrove Cay, and South Andros. The island has the world's third largest barrier reef, which is over 225 km (140 mi) long. It is affectionately known by Bahamians as the "Big Yard". Andros is the least densely populated of all the Bahamas, with a population of a little over six thousand. Most of these people live on the east coast of the island in the three major towns on the island; Nicholls Town and Andros Town on North Andros, and Congo Town, on South Andros.
Much freshwater comes from this island, with about nineteen million litres of freshwater being shipped to Nassau a day through the pumping station located in Morgan's Bluff. Andros has thousands of kilometres of freshwater rivers that come from rainwater collected in the many caves in the island's interior.
Andros lends itself well to terrestrial studies because its size correlates with its diversity. Savannah, coppice, swash, and mangrove areas are all accessible for field study. In both wetland and forested areas, a wide variety of endemic and North American birds have been included in long term bird counts. Reptiles include the endangered Bahamian boa,all five species of Caribbean sea turtles and variety of anoles. In the summertime, land crabs roam the pine yards and beaches. Along the coast compare the rocky shores to the white sand beaches, and ask to visit some excellent tidal flats in search of a variety of invertebrates.
Geologists are attracted to many features in the Bahamas, including the thick limestone foundation of the islands dramatically cut by deep channels. Andros is known for its 178 inland and 50 oceanic blue holes.
When people think of the Bahamas, they visualize white sand beaches, tropical breezes, and crystal clear water. Andros has each in abundance, but perhaps the most stunning aquatic feature is the barrier reef. Just one of several marine habitats, the reef runs the full length of the island, from a few hundred yards to one and a half miles off the eastern coast.
The Andros reef is the third longest in the world (second only to Australia and Belize), and is considered by many to be the most diverse and pristine. The reef has both fringing and barrier reef characteristics and supports a colorful and amazing diversity of life. It offers a tremendous variety of ten to 25 foot deep gardens abloom with both hard and soft corals, some of which emerge from the seas at low tides.