Next month I have a tourney on a navigable river system where 3 become 1. It is a major transport waterway, so it has all you would expect in the way of locks and navigation features. This will be a first for me on the river deal. I have heard that rivers will fish much different than lakes. So heres a question: With LMB and Spots as the target species what are some approaches to find the fish on a river system for a late post spawn/ summer bite.

It's all about the current.

Bass are bass no matter where you find them.  They will attack the same baits, but in a river system the current can be key feature.  For example you say it has locks etc.  If these are opened and closed to regulate the flow of water I would suggest fishing when they are open.

Other than that, look for structure, cover, and find the baitfish.

OH, one other thing.  Rivers will often have undercut banks at the bends.  These spots can be killer.

Another attempt that I use when fishing river is fish with the direction of the water flow. Fish will most likely be swimming in the direction of the current, I would rather have the bait swim in front of the fish than come at it from behind. Both work through.

Just like Avid said fish undercut banks, also fish eddies with slack current

I tend to cast upstream and let the current work a bait like a light jig head with twister tail grub back down stream for me keeping semi-slack line.  This works extreme well for smallmouth in my area.  Also I like to target wood and rock way more than grass and weeds when fishing rivers.  

More information about where this location is might help us give better advice.  Here's my general advice for fishing river system reservoirs in East Tennessee.

(1) Know your prey.  Are you better off targeting largemouths, smallmouths, or spots?  In TN smallmouth are great but they have to be 18 inches in most places which means you need to be catching really nice smallies to count 'em.  A 17 inch largemouth might be easier to find than a 18 inch smallie.

(2) Know the current schedule (if it's under generation).  Some spots will hold fish with no current.  Some will only hold fish when the current is running.  Find out where to get information about the planned generation schedule for the dams above and below the pool you're fishing.  The currents will be different if they are generating from the dam upstream of you versus downstream of you or from both.  Generation from the downstream dam only will pull some current and possibly drop the water level.  Generation from upstream will generate current and possibly raise the water level.  Generation at both dams will crank a pretty good current with perhaps no water level change.  The last Bassmasters magazine had a good article about reservoirs with dams, check it out.

I won't give advice about baits and such 'cause that's pretty wide open depending on where you live.  Hope the little information is helpful.  Be sure to report back and tell us how you did.

Cheers!