A sunken oil tanker, one of dozens on the bottom of Micronesiaâs Chuuk Lagoon is releasing streams of purple diesel bubbles. At the end of July, the oil slick was five kilometres long. Corrosion experts say the 52 wrecks in Chuuk Lagoon could collapse in a few years, yet no-one knows how much fuel was inside the vessels when they sank. The problem could take on astonishing proportions: more than 380 other tankers lie at the bottom of the Pacific. Bill Jeffery, a maritime archaeologist at James Cook University in Australia, is part of a team carrying out surveys of the Japanese shipwrecks in the Chuuk Lagoon. The wrecks are overgrown with coral, house a huge diversity of tropical fish, and attract tourists, who provide welcome income to the local population. Helped by the charity Earthwatch, the researchers have been studying the site since 2001, so that the Chuukese government can take steps to preserve it.