By September the flows should be down to very wadable levels.

Rock Creek and the Blackfoot are your best options for a lot of access and good wading. The Bitterroot has a lot of access points, but it also involves dealing with a lot of posted private land. If you are a really strong wader, you can solve the private property problems by crossing the river to stay within the high water mark, or you can go with watercraft. The Clark Fork well above Missoula has wadable water, but also poses access issues. Below Missoula, the Clark Fork is quite large, and is best fished from watercraft.

If you don't have watercraft suitable for both the Bitterroot and the Clark Fork, or don't want to use a guide, you are better off spending more ( most ) of your time on Rock Creek and the Blackfoot and scratching the Clark Fork.

The river maps can help on the Bitterroot, and the Blackfoot, to some extent, but you can just as readily get access information for those rivers by talking to the local fly shop folks - The Grizzly Hackle, Missoulian Angler, Blackfoot Outfitters, and Kingfisher. Rock Creek Mercantile can give you information on what's happening on their namesake water.

John