Looks like the common posters at this board do not have specific local knowledge for you.
I suggest you contact a local marina or boat club.
I agree with others, get a depth finder and local marine map however rivers can vary in depth fast. One bend you need to stick to the outside, the next inside. At least that is how it is where I boat.
I know where to go and where not to go in my area and I learned by talking to locals. Oh, and I learned the hard way a couple of times too.
I grew up on the Minnesota River . . . it is navigable from the confluence with the Mississippi to roughly Shakopee, MN for larger boats. The main channel is marked for tow traffic at least through the city of Savage. You may be able to go further but as everyone mentions, a depth finder is a must.