Scientists in Australia say the country's iconic Great Barrier Reef is experiencing its worst coral bleaching on record thanks to a rise in water temperatures.
Surveys of the reef that stretches for 2,300 kilometers off Australia's east coast showed 93 percent of the coral had some bleaching. The problem is worst in the northern part of the reef, where 81 percent is severely bleached.
The problem happens when warm temperatures cause the coral to expel algae, which turns it white and robs it of an important food source. If temperatures drop, the coral has a chance to recover.
Scientists said in some areas half of the corals in the reef are already dying.
The Great Barrier Reef is a World Heritage site that brings Australia $5 billion per year in tourism.