No, all you want is not depth and temp. Fishing Wabigoon and other similar lakes up there you need GPS and down image as well as a minimum, There are lots of times when the walleyes move off the feeding structure and disperse out onto the surrounding flats and they can spread out pretty widely and are often very actively feeding. Most of the places that you learn to catch walleyes up there are rock piles in like 20 feet of water, or flats surrounded by shallower good feeding habitat. I have learned that one of the things they do when they move off those rock piles is to cruise the flats looking for crayfish. Molting crayfish in particular. The can spread out up to 1/2 mile away and being able to mark them with a GPS helps put you back onto them as you drift.
Also, the down image or side image units will help you make sense of where those big smallies go when they are not up on the shallow benches hunting molting crayfish.
Finding walleyes with a fish finder is maybe more difficult when they are shallow. But... they usually move a little deeper in the middle of the day and spotting them then is much easier and the down/side image can be very helpful.
Get GPS and down or side image and learn to use them together with conventional sonar. I keep all three on my screen at once most of the time, and it really does help a lot in places where I'd not thought it could possibly be useful.
