There are a hundred patterns that work well to imitate the BWO hatch. The trout on the Pan are somewhat educated - as familiar with the Umpqua catalogue as any fly fisher or fly tyer.

The day that Jon, Fred and I experienced was nothing short of pretty silly. I tied on one fly in the morning and never changed it. I fished the surface all day with great success. The pattern I chose to fish was the Drymerger Baetis in size 20. It's not a difficult fly to tie and I will explain the steps.

Steps:

1. Tie in two tails that are the length of the shank.
2. Split tails to 35-40 deg.
3. Cut off about 3 inches of yarn and un-spin. When yarn is unspun pull apart.
   
4. You should now have two pieces that are about 1.5 inches each. Save one for the next fly. Spin one piece of the yarn up and notice the taper you have made. Tie in the smaller side at the tail. (it is easier to spin the yarn after tying to hook.)
   
5. Wind the yarn up the hook about ¾ of the way to the eye, and tie off.
   
6. On the top of the hook tie in small amount of Chickabou with tips towards the bend. The tips should almost reach the bend of the hook.
   
7. add small amount of olive superfine dubbing as a thorax leaving at least a space the size of the eye blank on the hook.
   
8. Fold the Chickabou over the dubbing and tie down.
   
9. Take that same Chickabou and now fold back towards the bend and tie down.
   
10. Tie in a small brahma feather and wrap two times and tie off.
    
11. Build thread head and whip finish.
    

The only advice that I offer to you is not to use any silicon based floatant. You're better off using a dessicant, like frogs fanny.

The fly was designed with the help of my fish-tank and a few dozen natural mayflies. I noticed what a mayfly looks like from under water during the emergence and as an adult. I started to tie accordingly, and came up with this pattern. It's kind of a 'tweener fly that works well in the film as well as a high floater.