Based in London, with a field site in Andavadoaka, this hugely impressive organisation coordinates teams of volunteer divers to work with local NGOs and biologists in marine-conservation programs that are spreading throughout the length of the reef, helping staunch its decline. Volunteering stints range from three to 12 weeks (£1900 to £4075) and include PADI scuba-diving certification.

Volunteering must be organised in advance through the London office.