Drowned (or submerged) reefs are tropical coral reefs that grew during previous lower sea-levels, and they now lie in depths greater than those typically associated with the vigorous growth of modern coral reefs. On Australia's Great Barrier Reef, an extensive line of drowned reefs are found along the outer-continental shelf in depths of about 40 to 70 metres. These images were taken from a research expedition in 2007 to explore these reefs using Australia's RV Southern Surveyor and an Autonomous Underwater Vehicle.