A Sword!
It turns out that the old object was an ancient sword! It was rusted beyond recognition, but it was still an incredible artifact to find in the shallow lake! Olivia was over the moon with her discovery, and it felt like she was a real-life adventurer!
Her father decided to help out, and they decided to put the sword in a bath to try and treat the rust on the sword. They wanted to see if they could bring their new artifact to its former glory.