Children's ghost story about a boy who meets his dead uncle in a YMCA swimming pool

I'm trying to remember a book I read in school many years ago. It was an English-language middle-grade/children's novel, probably a paperback.

The story was about a boy who swims at a YMCA pool. While swimming, he sees another boy underwater and eventually discovers that the boy is actually his dead uncle's ghost.

The uncle had drowned when he was a child, and this was a family secret. I vaguely remember that the uncle's death was connected to a water park or swimming trip. Another detail I remember (although I may be mixing things up) is that the boy's mother had been the uncle's girlfriend first, and after the uncle died she eventually married his brother (the boy's father).

I think the cover may have been blue, but I'm not completely sure. The ghost could talk to the boy somehow, and I remember the YMCA pool being mentioned several times.

I read this in a school library (in India), but I think the setting was in the US.

Does anyone recognize this book? I've been trying to find it for years!