What’s the mosquito sitch on these Minnesota lakes during summer?
If varies, and gets worse at night. Most of the time it isn't really that bad at all. If you are going to be out of the water, just wear bug spray or clothes that ward them off. Camp fires work great for keeping them away. People don't really ever notice them if they are swimming or tubing/skiing during the day, for example.
Personally, since our kids are nearly out of the house, we don't spend any time swimming really. I'm either fishing or doing a stroll around the lake in the pontoon. When I am fishing I am usually wearing long sleeves, like those fishing hoodies, and then a little bug spray on top of them to keep them away. On a moving boat, they won't get you much, so the pontoon strolls are nice.
The whole thing kinda gets overblown. Northern Minnesota, Northern Wisconsin, and Northern Michigan all have the same ecological profile, and they are all amazing in the summer. Minnesota does have the advantage of more lakes, of if you like water stuff, that's nice. Wisconsin and Michigan have way more access to the Great Lakes though. Duluth in MN is a super desirable place on a great lake, but definitely better in WI and MI if you like the big water 100 foot lake trout and salmon stuff.