LONDON — At the height of a sweltering summer, Saga Vanecek went paddling in a southern Swedish lake. And in the shallow waters, reduced by a long heat wave, she came across something astonishing.

She thought it was a stick, she told the news website The Local, and she was going to skim it over the water. But when she fished it out, it was a sword — about 33 inches long, black-brown with age and rust.

According to a Facebook post by her father, Andy Vanecek, she “lifted it high above her head, and shouted, as if she was Pippi Longstocking,” a Swedish storybook heroine, “ ‘DADDY! I FOUND A SWORD!’ ”