Simon Banks, general manager of reef protection for Great Barrier Reef Marine Park Authority, confirmed the 28 cubic metre spill, that occurred off the coast of Innisfail, to Greens senator Larissa Waters.
Australian Maritime Safety Authority (AMSA) had alerted the park authority of the P&O Cruises spill, he said, noting that Maritime Safety Queensland would have responded to the accident.
The report says that the spill occurred on August 26 after food waste was transferred to Pacific Explorer’s galley holding tank because of shortage in capacity in ship's food waste tanks.
Waste from the galley tank had then been discharged by engineers in the marine park. The vessel became aware of the accident late on August 27.
The hearing heard P&O Cruises reported the spill to AMSA but Great Barrier Reef Marine Park Authority had not been informed until September 4.
An investigation is ongoing.
Russell Reichelt, Great Barrier Reef Marine Park Authority chairman, earlier told Labor senator Anthony Chisholm that climate changes posed the greatest threat to the reef's health.
He added that possible El Nino weather system could "spark further coral bleaching on the reef this summer."
Half of the shallow cover coral of the reef was lost in the summers of 2016-2017 from severe weather and coral bleaching.
For other Pacific Explorer accidents and incidents see at the ship's CruiseMinus page.