The Marco Polo TT-Line passenger ferry ran aground south of the southern city of Karlshamn early Sunday, with the vessel’s 75 passengers safely evacuated.

Sweden’s coast guard on Thursday said the ship was still stuck and leaking oil, and it was unclear exactly how much oil had leaked.

The authority added it would likely take days before a salvage operation for the ship could be started.

“The oil spill… will require large and extensive resources for a long time to come and will soon affect all parts of municipal operations,” the Solvesborg municipality said in a statement.

Speaking at a press conference, Anders Borgman, crisis coordinator for the municipality, said the clean-up could last “up to a year,” according to news agency TT.

Earlier in the week, the coast guard said a streak of spilled oil stretched over five kilometres (three miles) out at sea.

However, by Thursday, aircraft could no longer detect oil at the surface as it had sunk and begun to reach the shores.

“Right now, everyone involved is working hard to recover oil from beaches and bays, where the oil lies among rocks in shallow areas,” the coast guard said in a statement.

It added that the work was hampered by poor weather conditions.

A criminal investigation has been launched and two people are formally suspected of “recklessness in maritime traffic” in relation to the accident.

Neither their identity nor nationality was disclosed.