Yeah the upper midwest would work well for him, but his fiance nixed it. I appreciate your position, my wife would want to move back to Chicago, but I've nixed that
I love Colorado, but it probably isn't for you. Steelhead and Salmon are out for one. There are some runs up from reservoirs but I doubt it is what you are looking for. There are bass, pike, etc. out here. A lot of people fish them in reservoirs (they call them lakes out here but us mid-westerners know the difference), but there are some in rivers. I haven't explored the bass fishing much, though I need to. There was a recent article about pike in the Colorado near Pump House/Gore Canyon. People are worried they will hurt the trout population.
There are a lot of people too. There are less populated areas. But of course the people come with advantages - amenities for one, but also jobs. Depending on what you do you might need to live near larger population centers. My wife and I both work in hospitals and she needs an academic medical center so larger cities it is. But as larger cities go, Denver is a pretty nice one