The coral is growing along the entire coast, just a few millimeters a year, and when it dies, it turns to stone and new coral grows nearby.

Local fishermen have known about it for years, because their trawlers often pull some of it up. Over the past few years, researchers have been diving to the deep in mini-subs to chart it and photograph it. They've found one reef after another, and want to make sure that oil exploration efforts don't damage it.

"The coral is gorgeous and some of the most special that Norwegian nature has to offer," Jan Helge Fosså of the marine research insitute (Havforskningsinstituttet) told newspaper Aftenposten. He's been leading the research group that has responsibility for the coral mapping project.

The world's largest cold water coral reef was found off Lofoten, the scenic archipelago that stretches into the Norwegian Sea west of Narvik. It lies at a depth of 300-400 meters about 110 kilometers west of Røst. The reef itself is about 35 kilometers long and three kilometers wide.

Environmental groups are also keen to preserve the coral reefs, with more than 1,000 of them lying outside Træna. WWF Norge claims they're endangered even though they're large, and is demanding better monitoring and protection for them.