But what brought it back to life? The answer lies on the outer edge of the reef.

 

Will Gadd is heading for an encounter with an invisible force of nature that waits in the same place all day, all night, and all year. It's both a killer and a giver of life.

 

“This is one of the most famous dive sites we have here. So we're at the top of Ribbon Reef Number 10. You see on the other side--You can see the wave breaking. That's the open ocean.”

 

Down here flows a monstrous current. It rips along the reef far faster than a human can swim. The only choice is to go with it. But what can kill a diver is also the lifeblood of this reef. It's called the East Australia Current, and it is the secret of how the Great Barrier Reef came back from the dead.

 

Over 100 miles wide, 1,500 feet deep, and it ferries southward about 30 million tons of water per second-- 2000 times the flow of the Mississippi River. It carries a constant resupply of coral larvae from other reefs in other oceans, ready to repair any damage that the reef has suffered, however big.