Just because it is summer, it does not mean all the walleyes are deep. I have a rule and that is always fish the shallowest part of the structure you are fishing especially if the weather is good. Clouds, wind, humidity and rain help make the shallow bite better. Here is an example: yesterday I was catching walleyes on a rock pile that topped out at five feet. It was a calm day without much humidity--most of the fish were caught in 28 feet. Today the weather changed--clouds, more humidity, and a nice breeze--the change in weather means I will check out the top of the reef first and then work my way down.
When the bite is good, the biggest fish will go shallow because they can. The smaller fish are a little more shy.