The Great Barrier Reef off the coast of Australia has been hit by the worst coral bleaching ever recorded, according to authorities. “The cumulative impact on the reef this summer was higher than in previous summers,” the marine park authority said on Wednesday.

According to the agency, aerial photographs show that about 730 of the more than 1,000 reefs are affected by coral bleaching. It is the fifth massive coral bleaching event in the Great Barrier Reef in eight years.

When the water temperature rises too much, the phenomenon of coral bleaching occurs. The corals then reject the algae that live within them, which is their primary source of food. As a result, the corals lose their color and are in danger of death. However, there is hope for recovery if temperatures fall and other factors such as overfishing and pollution are reduced.

The Great Barrier Reef is home to, among other things, more than 600 species of coral and over 1,600 species of fish. It has been suffering from repeated coral bleaching for decades.