Looks like mayflies are emerging from area lakes and streams. The mayfly is an interesting insect. The adults, which is what you are seeing, do not feed and only live for a few hours or days, just long enough to mate and the females to lay eggs back into the water. The emergence from the water is fairly well synchronized and only lasts a few days, when literally millions emerge nearly at once. They do not have functional mouthparts and do not bite. Most of its life is spent as a nymph in the water. Lewis and Clark Lake has big hatches every year but some are bigger than others.