Re: what is it?
Chuck, and Mike,
I think that a Dobson Fly has more of a delta wing when at rest. That sure looks like a stone fly but it's true that they like moving water as per iceclecreek's post. I don't remember stones on still water but there may well be populations that live in lakes that have a rocky shore line strata. So.............Mike, is the lake a rocky bottom near shore?
Something else I'd ask is, how big was the bug in the picture?