Australia’s National Coral Bleaching Taskforce has released its first comprehensive map of the Great Barrier Reef’s bleached corals—revealing that a large portion of the reef has been slightly to severely damaged.

Published after extensive dives and flyovers, the map paints a devastating picture of the damage that the Great Barrier Reef—a 2,300-kilometer string of reefs along Australia’s northeast coast—has sustained in recent months.

The bleaching is caused by abnormally hot waters warmed by El Niño and climate change. The temperatures cause corals’ symbiotic algae—their crucial food source—to short-circuit and become toxic, forcing the corals to expel it. Kicking out the algae turns the coral bone white and potentially sets it on a path to starvation.

The Great Barrier Reef is made