The boat was grounded on rocks on the seaward side of Holmes Wharf because it hit "shallow water on a low tide".
Maritime NZ spokesman Vincent Cholewa said no action was to take place against the skipper, the boat owner or the crewmate on the boat the night of the sinking.
The incident involved no injury or fatality and there was no evidence of drugs, alcohol or negligence, Mr Cholewa said.
"It appears to be an accident. We’ll take no further action."
In early February, Jane Marie ran aground on the seaward side of Holmes Wharf after it attempted to come into Oamaru Harbour late in the evening.
The two crew on board ended up in the water, were rescued and taken to hospital for treatment.
The Otago Regional Council ran an environmental clean-up for the sinking, but reported no harm to the Oamaru environment as a result of the stricken vessel.
Mr Cholewa said the the boat hit shallow water on a low tide.
"It was a surprise to them.
"It might have been caused by movement of silt or sand."
The owner of Jane Marie, Jeremy Hatherly, of Dunedin, said he had not been informed the investigation had concluded but said "it obviously was an accident".
He thanked "a lot of nice people in Oamaru" who had helped him out after the accident.
