I have a large amount of these flies around the small pond in my garden .
They do not seem to stray far from the water and alight readily on the surface, what I presume are Males seem to flit up land and flash their wings out like signal flags at I presume Females , which I also presume are laying in the water.
The nearest I can get to is Chrysops ?
What I really what to know is are they as harmless as they appear .
Photos not the clearest as taken through tubes.