Conditions so far this season have been ideal for the development of oak anthracnose.  

Although we can't be sure by viewing the photo, that's probably what's affecting the trees.  Bur oak blight symptoms are most prominent in late summer and fall.

Anthracnose can be unsightly, but healthy trees usually tolerate it and replace damaged leaves. 

Learn more here:

https://extension.umn.edu/plant-diseases/anthracnose-trees-and-shrubs

http://www.minnesotaseasons.com/Fungi/Oak_Anthracnose.html