Best marine Garmin GPS map for boating on the upper Mississippi river

Question

I recently bought a boat with a Garmin GPS unit installed. I looked it up, and it is a $900 unit, but the tracking and detail are terrible.

I boat near LaCrosse WI, and according to the GPS unit, half the time I am on dry land. Garmin says they do not have any software that is any better. Has any one purchased a add on map that works on the upper Mississippi river ?

Answer 1

Here is Garmin's web site to the Mississippi - not sure if it works with your unit.  If not you can try to find a card from them that does:

http://www8.garmin.com/cartography/g2vis...