I don't know whether these are gnats or something else, but they're really annoying.

I was in my yard yesterday working on power washing the fence (to get the mold off). When I was in the grassy areas, I was constantly bombarded by little flying nuisances. It's hard to count them, but at most times in my field of view I could see at least 30 buzzing around my head, with a half dozen landing on me at any given time. I could swat the air and hit at least six at a time, sometimes more.

Is there anything I can do about this? Can I do it myself or am I going to have to call someone? Are these gnats or something else?