Normally I take a picture next to a ruler so my memory/imagination is not a factor. Anyway this one didn't stick around long enough for that shot. I did look at the exif data for the image which allows me a rough calculation and I get about 5 mm +/-. My memory would have probably said 6 or 7.

That's pretty close to the size that I expected. Here's my best guess:

It seems pretty clear that it is a heptageniid. The eyes look as though they probably are contiguous or nearly so, which helps to rule out many potential genera. Compare it to the dun that Jason Neuswanger identified as Nixe inconspicua here. Imagine it molted into the clear-winged imago with the large eyes heavily fluoresced by bright light. You'll note in the comments that Jason is second-guessing his ID. I can't find anything that isn't consistent with a Nixe ID, but I have to add that I'm not familar with this genus, and I don't think Jason was either. That's always a handicap, so I can only commit to maybe Nixe, maybe Epeorus. (But I'm leaning toward Nixe, mostly because it doesn't look like any Epeorus I know.)

Another cool one, even if just a maybe! :-)