Marsh Bellflower?
Look at number 61 to the left of the page here...
http://www.carsoncity.k12.mi.us/~hsstudent/wildflowers/
Marsh Bellflower is definitely the closest I’ve seen. It is growing less than 20 feet from the lake. The stem looks similar too.
I find all kinds of wildflowers during my wanderings that I don’t recognize.