June 23, 2015 — Dane County
lagoon on the south end of Stricker's Pond in Middleton. Drive to the south end of Middleton St - it is a dead end. Walk 50 yards along the path. Stricker's Pond is on your right, the lagoon is on your left (south).
I saw it first on June 21 but did not get a photo until June 23. Bob Dubois confirmed the identification.