I don't know the title but I have the plot, and it is DEFINITELY not Startide Rising. It is a really old book pre-90s for sure, maybe even older.
The humans have created genetically engineered dolphins to fight off an alien threat, but this book takes place after that, after a while the humans and the super intelligent dolphins have a rift forming between them because there has been very little contact between the two species for years.
It is a stand alone book and not part of series. If you know anything then thank you for your answer.