I live twenty minutes south of Grand Rapids.
I enjoy Lake Michigan charters for lake trout and (allegedly) salmon. Salmon might already be moving into the rivers to spawn in southern MI in August. They are more likely to be out in the big lake the further north you go. Lake trout are always available in the big lake and plenty of folks offer charters out of all the lakeside towns: saugatuck, Holland, grand haven, pen****er and ludington are all within reasonable distance from GR to book a charter.
As mentioned, pere Marquette river is a good option for rainbows, Browns, and maybe salmon by August, but there's lots of small stream fishing for trout if that's your thing. Hell, I have a trout stream in my backyard.
The Lookinglass river a little further east is reputed to be 'world class ' smallmouth fishing but I've never fished it.
You are never more than about 3 miles from a navigable body of water, so there's just too much to mention it all. Reply back with what you really would like to fish for, and I'll get you some more detailed info.
Ridin' 'cross the desert. . .