Maritime New Zealand has begun an investigation into the sinking of the cruise boat Waverley in Doubtful Sound last Friday.
A Christchurch Maritime NZ investigator will interview the boat's skipper, Te Anau-based owners Clint Tauri and John Harris and some of the eight overseas passengers who were rescued without injury, hours before the boat sank.
Maritime NZ spokeswoman Sophie Hazelhurst, of Wellington, said the inquiry would look at what safety lessons could be learned.
"Whether or not there will be a report depends on what is discovered. If there was a hazard that some action needed to be taken, then a report would be compiled with that recommendation in it."
Concerns were raised about the environmental impact of spilling fuel which had created a 1.7sq km oil slick off Matai Island.
The boat had an estimated 700l of fuel on board when it sank.
However, shoreline and aerial inspections by Environment Southland and the Department of Conservation (Doc) on Saturday found only tiny amounts of diesel were bubbling up intermittently, and that could continue for days or weeks.
Regional on-scene oil spill commander Kevin O'Sullivan said tourist operators in the sound would monitor the water around the submerged boat.
If larger amounts of oil surfaced, or birds were found to be affected, a response could be mounted immediately.
Doc wildlife adviser Pete McClelland said the spill from Waverley was a "best-case scenario", given what could have occurred.
The impact on wildlife had been minimal, he said.