This is a very good question!
On pool 4 the vast majority of the walleyes move back out into the lake after spawning. Some do remain in the river as resident fish.
I prefer to stay in the river fishing the backwaters and side channels where current concentrates the walleyes. Out on the lake the walleyes are much more free to roam with no current (no significant current) to dictate their location or feeding patterns. This makes the walleyes harder to pattern in my opinion. One day you knock the heck out of them. The next day the fish are nowhere to be found.
If I grow tired of fishing uppper pool 4 in the river I’ll run down and fish the wingies south of the lake. Again, back in an area where the current dictates fish location making it a little easier to pattern the fish.
There’s an enormous number of big walleyes out in the lake and at certain times of the year the odds tip in the favor of the angler. There are a couple patterns I do enjoy fishing out on Lake Pepin. The month of June and July can be very consistent for the trollers pulling cranks behind boards for susupended fish. In the fall, starting in mid to late september guys casting crankbaits and hair jigs to rip rap or natural rock shorelines can consistently catch numbers of big walleyes.
But day in, day out, the river is the place for me. The current dicatates where the fish will be and that narrows the search area down considerably.
If I needed to catch 40 fish tomorrow I’d go hit the lake for sure. The numbers are certainly there. If I needed to catch 20 fish tomorrow with 2 of them 6 Lbs plus… I’d hit the backwaters just above Pepin.
Please pass the willowcats.