The Viking Sky cruise ship that had to be evacuated off the coast of Norway over the weekend had low oil levels that led to engine failure, according to the Norwegian Maritime Authority, which has been investigating the incident.

Norwegian officials opened an investigation into the incident Monday, and the NMA has been working with Viking Ocean Cruises and Lloyd's, the ship's classification society, to identify why the cruise ship suffered a power blackout Saturday.

Lars Alvestad, the head of Norway's Maritime Authority, said Wednesday that low oil levels were the "direct cause" of the engine failure that stranded the Viking Sky on Saturday.

The NMA indicated in a press release that while oil in the tanks was relatively low, it was within set limits. But as the ship crossed rocky seas, movement of oil in the tanks triggered an alarm. Norwegian media reported gusts up to 43 mph and waves over 26 feet.

"The heavy seas in Hustadvika probably caused movements in the tanks so large that the supply to the lubricating oil pumps stopped," Alvestad said. "This triggered an alarm indicating a low level of lubrication oil, which in turn shortly thereafter caused an automatic shutdown of the engines."

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Viking Ocean Cruises said in a statement that the company is revising procedures to ensure the issue doesn't happen again.

"We have inspected the levels on all our sister ships and are now revising our procedures to ensure that this issue could not be repeated," the statement said. "We will continue to work with our partners and the regulatory bodies in supporting them with the ongoing investigations.”

The Viking Sky sailed from the northern city of Tromso over the weekend bound for Stavanger in southern Norway when the ship had engine failure, started listing dangerously, then took in water.

Viking Sky's crew sent a mayday call and anchored in heavy seas to keep the ship from being dashed on rocks in an area known for shipwrecks. Five helicopters lifted 479 passengers off with winches.

The rescue operation ended Sunday when the engines restarted. The ship traveled under its own power to a Norwegian port with nearly 900 passengers and crew members still onboard.

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Contributing: The Associated Press