Oops.
WeirsCAM doesn't have the correct file name suffix for posting here.
They look like
chironomid midges -- a non-biting, mosquito-looking, flying insect.
They are a harbinger of um...um...
tainted water.
Habitat described, and sketch/drawing of a midge:
http://muextension.missouri.edu/expl...sts/g07402.htm