They are dancing in my garden as well brionon, just above the bird bath, so am leafing through books for ID. Two possibles.
Non biting midges are often mistaken for gnats, but they have no mouth parts. Since the adults cannot feed they don't live long - a week to two months and measure an eighth to half an inch in length. Found near water (or dancing over birdbaths!)
The second are the Gnat group. If you can hear them humming at dusk, that's the female gnat. Eggs laid in still water etc. etc. Rest is boring and doesn't fit in with your description, so my money's on the Non-biting Midge.