I saw a lot of these at Pass Lake this past weekend, but they were wriggling around in the surface film just like an emerging chironomid. The only problem was that they weren't hatching, just hanging out. Looked like maggots but more wormlike, 1/4" to 1/2". This was near the shore. Maybe I just never notice things but in 15 odd years of bobbing around in a tube I've never anything like this before before.