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A shark appeared in a New Zealand river over the weekend, shocking onlookers and prompting authorities to alert locals to steer clear of the unusual visitor.

A local woman spotted a dorsal fin moving upstream through the Whanganui River, one of the country's largest rivers, about 5 miles (8 kilometers) upstream from the ocean, the New Zealand Herald reported.

"My mum saw it first and said 'what the hell is that'?" Kelly McIntyre, 26, told the New Zealand Herald. "We got binoculars and sure enough I saw a big triangle sticking up out of the water. It was dark grey or black and was quite clearly a dorsal fin," McIntyre said.

The women saw children fishing near the water, and immediately alerted the police of their shark sighting.

A representative from the local conservation department confirmed that the shape in the water was indeed a shark, although it's not clear what species made the long trek up from the Tasman Sea into the town of Wanganui.

A police officer said the shark was between 3.3 and 5 feet (1 and 1.5 meters) long.

According to the International Union for Conservation of Nature, the organization that assesses the status of animal populations worldwide, up to one-third of the planet's shark species are threatened with extinction .

A large crowd gathered to see the spectacle. The shark was last spotted just north of a bridge over the river.

"I've lived here all my life and never heard of sharks swimming up the river," McIntyre said. "It's crazy."