WWF Cook Islands Project Coordinator, Jacqui Evans says she has observed complete bleaching of about 30 per cent of corals in Rarotonga lagoon. "But we haven't done any quantitative surveys," she says. Cook Islands dive master, Eric Bateman says bleaching has also been observed on the outer reef slope of Rarotonga. He says it has been an unusually long summer. "Water temperatures have only just started to cool down, and it's nearly May," says Bateman. Resident marine biologist, Steve Lyon says, it's likely the islands in the northern group of the Cook Islands are worst hit. "And the lagoon on Rarotonga is probably suffering more than the outer reef slope." Ministry of Marine Resources staff are doing bleaching surveys on the reefs of Aitutaki island and on the uninhabited atoll of Manuae. These islands are located 140 miles north of Rarotonga. Coral bleaching could become an annual event, scientists warn.