The corps makes a nice map- more for navigation but i bought one that covers all of the river from the headwaters to where the locks stop- it has a cd rom and a hard copy. It is large and cumbersome at times, but works well. There are not any depth readings on it.
Also, I ran into a guy fishing the Federation tour out of minn last year (or maybe the year before- the regional was held on 9 and 10) who had some color coded depth maps he downloaded from the net (he claims to have spent over 100 hours searching) which showed which backwaters held water. Of course, he was unable to give me a short cut to finding it and I dont have the time.
Anyway, try the corp website or contact them for a hard copy. Good luck, and if you find something better let us know.