Image used for illustrative purpose. Natalie Friere, a diving and snorkelling guide, swims through a natural archway in an area called the 'Coral Gardens' located at Lady Elliot Island and 80 kilometers north-east from the town of Bundaberg in Queensland, Australia, June 10, 2015. UNESCO World Heritage delegates recently snorkeled on Australia's Great Barrier Reef, thousands of coral reefs, which stretch over 2,000 km off the northeast coast. Surrounded by manta rays, dolphins and reef sharks, their mission was to check the health of the world's largest living ecosystem, which brings in billions of dollars a year in tourism. Some coral has been badly damaged and animal species, including dugong and large green turtles, are threatened. UNESCO will say on Wednesday whether it will place the reef on a list of endangered World Heritage sites, a move the Australian government wants to avoid at all costs, having lobbied hard overseas. Earlier this year, UNESCO said the reef's outlook was "poor". Picture taken June 10, 2015. REUTERS/David Gray - RTX1IFE1

Dried coral lies on a beach as the sun sets on Lady Elliot Island located 80 kilometers north-east from the town of Bundaberg in Queensland, Australia, June 10, 2015. UNESCO World Heritage delegates recently snorkeled on Australia's Great Barrier Reef, thousands of coral reefs, which stretch over 2,000 km off the northeast coast. Surrounded by manta rays, dolphins and reef sharks, their mission was to check the health of the world's largest living ecosystem, which brings in billions of dollars a year in tourism. Some coral has been badly damaged and animal species, including dugong and large green turtles, are threatened. UNESCO will say on Wednesday whether it will place the reef on a list of endangered World Heritage sites, a move the Australian government wants to avoid at all costs, having lobbied hard overseas. Earlier this year, UNESCO said the reef's outlook was "poor". Picture taken June 10, 2015. REUTERS/David Gray - RTX1IFFP

Oliver Lanyon, senior ranger in the Great Barrier Reef region for the Queenlsand Parks and Wildlife Service, takes photographs and notes during an inspection of the reef's condition in an area called the "Coral Gardens" located at Lady Elliot Island and 80 kilometers north-east from the town of Bundaberg in Queensland, Australia, June 11, 2015. Picture taken June 11, 2015. REUTERS/David Gray/File photo - RTSUAP3

Image used for illustrative purpose. A tourist snorkels above coral in the lagoon located on Lady Elliot Island and 80 kilometers north-east from the town of Bundaberg in Queensland, Australia, June 9, 2015.

A large piece of coral can be seen in the lagoon on Lady Elliot Island, on the Great Barrier Reef, northeast from Bundaberg town in Queensland, Australia, June 9, 2015. REUTERS/David Gray/File photo - RTX2EQUT

Oliver Lanyon, Senior Ranger in the Great Barrier Reef region for the Queenlsand Parks and Wildlife Service, takes photographs and notes during an inspection of the reef's condition in an area called the 'Coral Gardens' located at Lady Elliot Island and 80 kilometers north-east from the town of Bundaberg in Queensland, Australia, June 11, 2015. REUTERS/David Gray/File photo - RTX2ARKU

Huts that form part of the Lady Elliot Island Eco Resort can be seen where a turtle digs for food amongst the coral in the island's lagoon, located 80 kilometers north-east from the town of Bundaberg in Queensland, Australia, June 9, 2015. UNESCO World Heritage delegates recently snorkeled on Australia's Great Barrier Reef, thousands of coral reefs, which stretch over 2,000 km off the northeast coast. Surrounded by manta rays, dolphins and reef sharks, their mission was to check the health of the world's largest living ecosystem, which brings in billions of dollars a year in tourism. Some coral has been badly damaged and animal species, including dugong and large green turtles, are threatened. UNESCO will say on Wednesday whether it will place the reef on a list of endangered World Heritage sites, a move the Australian government wants to avoid at all costs, having lobbied hard overseas. Earlier this year, UNESCO said the reef's outlook was "poor". Picture taken June 9, 2015. REUTERS/David Gray - RTX1IFGL

Peter Gash, owner and manager of the Lady Elliot Island Eco Resort, snorkels with Oliver Lanyon and Lewis Marshall, Senior Rangers in the Great Barrier Reef region for the Queenlsand Parks and Wildlife Service, during an inspection of the reef's condition in an area called the 'Coral Gardens' located at Lady Elliot Island and 80 kilometers north-east from the town of Bundaberg in Queensland, Australia, June 11, 2015. UNESCO World Heritage delegates recently snorkeled on Australia's Great Barrier Reef, thousands of coral reefs, which stretch over 2,000 km off the northeast coast. Surrounded by manta rays, dolphins and reef sharks, their mission was to check the health of the world's largest living ecosystem, which brings in billions of dollars a year in tourism. Some coral has been badly damaged and animal species, including dugong and large green turtles, are threatened. UNESCO will say on Wednesday whether it will place the reef on a list of endangered World Heritage sites, a move the Australian government wants to avoid at all costs, having lobbied hard overseas. Earlier this year, UNESCO said the reef's outlook was "poor". Picture taken June 11, 2015. REUTERS/David Gray - RTX1IFDJ

Peter Gash (L), owner and manager of the Lady Elliot Island Eco Resort, snorkels with Oliver Lanyon and Lewis Marshall, Senior Rangers in the Great Barrier Reef region for the Queensland Parks and Wildlife Service, during an inspection of the reef's condition in an area called the 'Coral Gardens' located at Lady Elliot Island in Queensland, Australia, June 11, 2015. REUTERS/David Gray/File Photo - RTX2ARGW