It was discovered in 1997 by a Californian sailor, surfer, volunteer environmentalist and early-retired furniture restorer named Charles Moore, who was heading home with his crew from a sailing race in Hawaii, at the helm of a 50ft catamaran that he had built himself.
For the hell of it, he decided to turn on the engine and take a shortcut across the edge of the North Pacific Subtropical Gyre, a region that seafarers have long avoided. It is a perennial high pressure zone, an immense slowly spiralling vortex of warm equatorial air that pulls in winds and turns them gently until they expire. Several major sea currents also converge in the gyre and bring with them most of the flotsam from the Pacific coasts of Southeast Asia, North America, Canada and Mexico. Fifty years ago nearly all that flotsam was biodegradable. These days it is 90 per cent plastic.