$2m undertaking for reef waste spill

Carnival Australia has been compelled to provide a "$2.1 million undertaking" after spilling 28,000 litres of liquid food waste into the Great Barrier Reef's protected waters.

The Australian Maritime Safety Authority detained the Pacific Explorer cruise ship on its way back to Sydney in early September until it guaranteed the amount, which was equal to the maximum fine available, an AMSA spokesman told AAP on Thursday.

The Great Barrier Reef Marine Park was notified of the accident one week after the cruise company self-reported it.

An investigation is currently underway.

A Senate estimates hearing was told of the incident last month, after Greens senator Larissa Waters asked executives from the Great Barrier Reef Marine Park Authority what occurred.

Senators were told AMSA had alerted the marine park authority of the P&O spill, and Maritime Safety Queensland responded to the incident.