The mammoth United Nations (UN) Oceans Atlas project, an interactive map of the sea, is now available online.

The website was conceived a decade ago at the 1992 Rio de Janeiro Earth Summit, and has been worked on for the past two and a half years at a cost of $500,000.

But on its first day the site experienced overload. "Sorry the system is way too busy. Please come back later," was a frequent, frustrating note for visitors.

Once fully operational, the site will offer maps of the seas and help governments plan for future coastal changes, the UN said. China, The Netherlands, Bangladesh and other low-lying coastal regions are all currently believed to be under threat from tidal rises.

The site also aims to target over-fishing, and quotes the UN Food and Agriculture Organisation's (FAO's) contention that all 17 of the world's major fishing areas have either reached or exceeded their natural limits, with nine in serious decline.

Dr Jacques Diouf, director general of the FAO, one of the Oceans Atlas's founding partners, said that the site was crucial to "sustaining life on earth".

"This important new tool will help co-ordinate and harmonise the work underway in various parts of the UN and in national agencies, academic institutions and other organisations, and will serve a major role in moving the world toward the sustainable use of oceans for food security and human development," he said.

Links to other marine life sites will also become available.