There's about a thousand must fish spots between the Clark and the catfish rendezvous.
With that said...and no offense to the catfish...but the last thing I'd be worried about if I was standing on the banks of the Clark are catfish. You've got one of the greatest trout fishing rivers in the nation right at the tips of your toes.
What kind of fishing do you like to do? Seriously...there's tons of options.
I'd drive highway 12 from Missoula through Idaho and trout bum my way back to Lyons.

It's an incredible drive too.