In 1976 I read a children’s full length softcover novel about a boy who moves to the country.  A girl lives nearby and she claims she can do anything as well as he can.  He has a weight set and can lift the heaviest weight.  She can lift it, too.  They visit a man who lives on a houseboat on a nearby lake.  “How deep is the lake?” he asks.  “Pretty deep,” she answers.  “A car went in it once.”  The girl sprains her ankle and the boy helps her home.