Philippa Pearce's Minnow on the Say is a lovely children's book all about friendships, families, treasure hunting and history all linked together with a canoe called the Minnow and a river called the Say (a barely disguised Cam).
It is made even better by the wonderfully atmospheric drawings of Edward Ardizzone who is one of the all time great illustrators of children's books.
It was her first novel and the start did a feel a bit stilted and even slightly dated. But the story soon gets going driven by the twists and turns in the search for the lost treasure, with the main clue the following few lines:
When Philip came to the single Rose
Over the water
The treasure was taken where no one knows
None but my daughter
A real treat.