GA 400 / Alpharetta / Roswell / South
From Alpharetta take 400 S and exit Northridge. R on Dunwoody Pl, R on Roberts Dr. Chattahoochee Natl Forest / Park. They've got an info store with maps of the river. I've gone wading while fly fishing for trout. Rainbow and Brown. There are deep parts farther south. If you take Roberts past the park it ends at Roswell Rd. Take a R on Roswell, you almost immediately cross the river, take your next right on River Rd. There's a park up on the right. Also, taking River Rd left has a park pretty far down, one closer and some public access. There's a huge lake at the end of River Rd in this direction. Forgot to add that there's a lake in the National Forest as well. Although I wasn't too serious, I know you can fish the Chattahoochee all the way down to the city. There's a dam which I heard had the Bass you referred to.
That's about all I remember. And, depending how far out 400 you are, just keep heading N and you'll hit Lake Lanier.