More than 132 feet below sea level, a diver was removing abandoned fishing nets from a shipwreck in the Mediterranean Sea when he had an encounter that would be the stuff of many people’s nightmares.

Somewhere between the white beaches of Sicily and the dramatic coastline of Tunisia, Derk Remmers was working as a volunteer when he came face to face with a great white shark.

As a member of Ghost Diving Foundation, a charity run by technical divers specialized in the removal of lost fishing gear and debris from the waters, Remmers often retrieves ghost nets – former fishing nets left at sea – before they become deathly traps for marine life.

“Scientists say that around 3 to 10% of all fishing gear is lost in any given year, in the oceans of the world,” Remmers told CNN Monday. “And if you could imagine how many fishing boats come out of any harbor, this is a huge amount.”

A shipwreck covered in ghost nets, which can trap marine animals. Derk Remmers/Ghost Diving/Healthy Seas