wow, sounds like you need an emerger pattern, sparkle dun perhaps. Of course that's if you happen to be fly fishing, otherwise I would imagine that there are various fish feeding on the mayflies so maybe a weightless fluke to try for the larger fish capitalizing on the opportunity. If you happened to have a couple flies with you and could tie on a dropper off a topwater bait maybe you could get a fly drifting by with spinning gear but that's a lot of work so either the fluke or a chugger to cause a little surface disturbance to trigger a competitive bite.
so whad'ya do?