Midges (Order Diptera, Family Chironomidae)

These flies are similar in appearance to mosquitoes, but do not bite.  Their feathery antennae help to distinguish them from mosquitoes.  Also, their larvae (longish grub/maggot-like) are capable of living in flowing streams, where mosquito larvae require still, standing water.  They compose a large percentage of the diets of trout and fisherman tie (fishing) flies to mimic their appearance.  Swarms of them are common above streams and lakes.

(Thanks to Brian Feldhake for identification.)