I fish the Wharfe a lot. For example, the season opened on my home water on the 28th March and I have been out 5 times since then. The Large Dark Olives are hatching and some days it can last for 4 hours and the fish are really on them at the moment. I have had quite a lot of fish and all caught on this pattern:

Hook: The one shown is a Tiemco 103bl, I have now swapped this to a Kamasan B525, Both in size 16 & 16
Thread: Pearsalls Purple (Modern) waxed.
Body: 2 strands of heron herl ribbed with very fine gold wire. Need to be able to see the thread between the turns of herl.
Hackle: Very pale blue dun hen hackle.
I have watched closely the emergence of many LDO's over the past week and this fly, when wet, is a very close resemblance in colour and translucency. I fish it up and down and it is at its most deadly when cast up from a rising fish (a metere) and let swing in front of it.
The takes are solid.
This is the quality of fish so far this season:

Hope you enjoy.