This extremely tiny fly was puzzling to identify. I collected it from a sparse mating swarm just above the surface of the river. It just doesn't have the "look" I'm used to seeing in Chironomids, but the key characteristics in Merritt, Cummins, & Berg point that way.
apparently with 4 segments, antenna with 6
-I can't see any ocelli
and wing venation
doesn't seem to match Axymyiidae
-Costa definitely ends at or near apex
of the wing (pictured)
-Obvious characteristics and wing venation
rule out a few other things
seems like a possibility due to the broad wings, but bugguide says they're supposed to have more antennal segments (eleven, though a different source says some have ten, at least in the Southern Hemisphere).
with median longitudinal
groove (pictured) rules out Ceratopogonidae
So my guess is some kind of chironomid from a genus that doesn't have the classic midge look. There are some like that.