It is believed that perhaps it was the Fox river and not Two Hearted which Hemingway fished, but Big Two Hearted gave a better romantic feel to the story. That was according to an owner of a fly shop just outside of Petoskey Mi and also by a literature professor at Michigan State.
This summer, I am going to actually be fishing both rivers in an attempt to connect with what Hemingway saw. The U.P. doesn't change very much and from what I have been able to gather, both rivers are remarkably like they were when the story was written. This is actually a working trip as I am doing this for a book I am writing and have already generated some publishing interest. Should be exciting.