Can Anyone Help Identify This Story?

Hello everyone this is a longshot but maybe you can help. My dad read me a really cool story in the early 90s and I can't for the life of me remember the title or author. It was about a boy who somehow became stranded somewhere and found a building that had a half -finished or broken mosaic that he repaired. He also befriended a dolphin and named her Minerva. Can anyone help me out with the title and author of this story? Thank you for any help you can give

 

Sounds a bit Greek to me