I may be wrong, but I from what I can tell, those "dead bugs" on the surface are just the carcasses from the fish flies. those are the "wigglers" that come out of the mud at the bottom of the lake. The same wigglers we buy for ice fishing bait. They come to the surface, then they turn into a "beautiful fish fly", like a "beautiful butterfly" coming out of it's caccoon. The fish fly lays eggs, the eggs sink into the bottom mud of the lake and hatch next year.
The only purpose a fish fly has in life is to reproduce, and that's it. They don't even have a mouth from what I understand. They lay their eggs, fly away and die!!! What a life, huh? LOL