You might consider camping a night or two on River lake, there are a few nice campsites. The southern island campsite is a favorite of mine, for several reasons. We had pretty good luck with walleyes on River lake on a mid July trip several years ago. There is a point just south of the River Lake campsite we stayed at, where the river narrows - you might want to give that a try for walleyes. It's marked with an orange dot on the map of the area from this site. Good Luck.
Here is a trip report if you are interested:
Kawishiwi entry to Malberg to River Lake and back