Michael Thompson posted pictures of breeding grebes from Lake Osakis on the Minnesota Birding facebook group on Sunday evening, and when I wondered if he had seen any Clark's, he looked through his photos and was able to post one with an obvious CLARK'S GREBE.
It's not clear exactly where this bird was since his friend was driving the boat and Michael was not tracking the exact location with each photo and breeding group. (Unfortunately the Todd/Douglas Co. line runs right through Lake Osakis.) It is also not clear if this bird is breeding - it was in with breeding birds and the photo shows it among nests, but without more details I don't think breeding will be substantiated.
This species has been found at Lake Osakis on a number of occasions, and folks heading that way may want to spend some time scoping the grebes present.