The future of the Great Barrier Reef is again in the spotlight, after the federal government approved the construction of the biggest coal mine to ever be built in Australia.

Environmental groups say the Carmichael mining project in Queensland's Galilee Basin will increase dredging and shipping in the reef, drain local water supplies and ultimately release 130 million tonnes of carbon dioxide into the atmosphere every year.

Environment minister Greg Hunt says he has imposed the strictest possible conditions on the project, which will provide electricity for up to 100 million people in India.