"A spring. And what’s actually coming out of this is fresh water. You can drink. You see this stuff bubbling out? This is what the traditional owners of this place call 'buiur bindi'—'fresh water in the ocean'." 

 

The locals call them "wonky holes", fresh water springs in the middle of the sea. 

 

"And it’s a really weird feeling in there. You’re in the ocean here. You really think by all means all the water here should be salty, and it’s not."

 

But where does the fresh water come from?

 

There are at least 200 wonky holes. The biggest are up to 60 feet across, and some can be found 20 miles out to sea. The clue to their origins lies in their location. They are found opposite the mouths of rivers, because hidden below the surface are underground rivers from an ancient past. 

 

"It’s an evidence that at some point in the past, wherever we have the Great Barrier Reef nowadays, it still was not water, it was all land."

 

Today, below the surface are channels, carrying fresh water out to the sea. This hidden network was created during the last Ice Age. This whole place was transformed. The sea level dropped by 420 feet, leaving just the rivers flowing across this newly created land. They turned the seabed into a verdant landscape where trees and shrubs flourished. This amazing transformation happened six or seven times in the last 150,000 years alone. This is the Great Barrier Reef’s alter ego—a world that has come and gone with every Ice Age. 

 

Surprisingly annihilation has been good for this reef. Each time the sea rises up again, the coral builds a new layer on top of the rubble from the old reef, another level on this limestone city. So with every wipeout, the reef has ended up even bigger.