Hi', Paul.
At this time of year, there aren't many different species of aquatic fly emerging anywhere, and the greater diversity will be on rivers.
On still waters, midges will be the main movers. Their pupae, 'buzzers', on reaching maturity will be moving up the water column in preparation for emerging, so, as has been suggested, it could be midge pupae that are attracting the fish. They tend to rise and fall, and their characteristic waggling movement will attract fish.
The relatively few upwinged species, lake olive, pond olive, claret and sepia dun, caenis etc may well be present in larval form, but they'll be on the bottom or in any greenery that is still alive.
Some of the more hardy, late season sedges might also hatch, and if your lake has an inflow, there could be the odd little stone fly around; and there could be terrestrials coming off the banks. But, the pickings are becoming fewer and farther between for the trout.
Fortunately, in addition to midge pupae playing at elevators in the water, there could be a fair few corixae about. They are shallow water inhabitants, they have no choice, as they come to the surface for air, and are very vulnerable as they paddle up and down, collecting air. Snails, where they exist, are there all year round, also, and there are species which also come up for air -- pulmonate snails. Occasionally, trout may be seen sipping at

the surface or bulging gently, in the absence of visible fly life, and they can be taking snails.
I've taken rather a long time to make the case for fishing buzzers, at this time of year, but I think it helps if you know something about the options, and there aren't a lot. The fry of other species is one option, but rises to them are usually quite spectacular.
Downstairs, an under-valued nymph is happily chomping away -- the damsel.
They are essentially bottom food just now, but they are pretty important in
some waters, as are hoglice and shrimps. So the options in the basement are generally better than those in the penthouse. Oh' yes, and caddis are a year-round option, also in the basement, but these bottom food sources are not generally found at great depth. Algae, weeds, and plant waste, the staple for many larvae, are vailable where there is good light penetration.
Hope that helps, wthout confusing. TerryC
PS Stewart, the Pirate, obviously likes the washing-line method of fishing in the top layers of the water column, and it is a great way to present both buzzers and nymphs to fish that are making visible disturbance. Go for it.
