An eight-year-old girl went for a dip in a Swedish lake and returned wielding an Iron Age sword.

Key points: A local museum described the find as "spectacular"

A local museum described the find as "spectacular" Experts said the weapon was up to 1,500 years old

Experts said the weapon was up to 1,500 years old It was found complete with a scabbard made of wood and leather

Young Saga Vanecek was swimming with her family in southern Sweden's Lake Vidosten when she stumbled upon a long metal object.

The Jonkopings Lans Museum said in a statement this week that the discovery was "spectacular".

"The sword is in total 85cm long and exceptionally well-preserved, including a scabbard made of wood and leather," it said.

"It has tentatively been considered from the Iron Age, that is at least 1,000 years, perhaps even 1,500 years old."

The museum said Saga found the relic in about half a metre of water.

They were not sure how or why the weapon ended up in the lake, but the Jonkoping County Museum and other organisations plan to investigate the area soon.

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The Vanecek family are also curious about the sword's history.

"Fantasies abound as we wonder what happened so long ago which led to a sword, in its scabbard, being lost to the bottom of the lake," dad Andy Vanecek said on Facebook.

"Did someone fall overboard, or through the ice during a winter trek? Was a wealthy noble buried in the lake, as from a scene in Game of Thrones? The mystery will forever be known only to Lake Vidosten."

He described his daughter's dramatic July 15 discovery on social media.

"Just minutes before the opening kick of the battle between France and Croatia in the 2018 Soccer World Cup in July, there was a reminder of a possible battle from over a thousand years ago," Mr Vanecek said.

As young Saga emerged from the waters, "she picked up the object, lifted it high above her head, and shouted as if she was Pippi Longstocking, 'DADDY! I FOUND A SWORD!'," Mr Vanecek said.

"As she held it high, gravity bent the fragile, over thousand year old weapon, and it was then that [I] realised that it actually was a sword."

An archaeologist visited the scene the next day and "with goosebumps on her arms," examined Saga's find, Mr Vanecek said.