A humble suggestion Zen,oh wise one.Possessor of infinate knowledge.
If the "Secret Lake" is the one we fished together,consider that those swirling raises from large fish may have not been takes of Damsel nymphs at all.
I fished that same rise a few days before you and threw many fine damsels to no avail.The water was rife with returning Chronomid Adults and I think they were porposing for them. I had no size 20 dry midges,don't fish that hatch anyhow as my eyes have failed me.