A 3D printer processes a ghost net during the exhibition "Second Nature" in Athens, Greece, on May 31, 2018. The ghost nets, the deadliest ocean trash and a major environmental threat worldwide, were transformed into 3D printed seashells in an exhibition entitled "Second Nature" held in Athens to raise awareness on marine plastic pollution. It is quite common for fishermen to lose or abandon their fishing nets in the sea -- these are the so-called ghost nets. They remain on the bottom of the sea for years forming dangerous traps for fish and marine mammals. (Xinhua/Marios Lolos)