This was taken from the Blue Ribbon Flies Newsletter:

"Watershed Treatment

Permanent Waterproofing Liquid

Watershed is one of the most exciting new products ever introduced. Nothing compares to this permanent waterproofing agent for flies, materials, dubbing, feathers, yarns, leaders, braided loops and fly lines.

Watershed will not leave oil rings or residues of any kind on the water surface, will not change colors or the texture of tying materials, and is completely odorless and colorless. It can be applied directly or dabbed on with fingers. One drop is all that is needed to pre-treat your flies. Craig pre-treats every fly he ties, and you can guess how many hundreds of dozens that is, and the bottle seems to last forever!

When cured, Watershed has a specific gravity lower than water and will make virtually any dry fly material float like a cork. In tests conducted by Hareline Dubbin, few if any dry fly materials, including deer hair, were found which did not float for days on end. To use Watershed, simply add a drop to your flies, materials, lines, leaders, tippets (or whatever). Allow to dry 24 hours. Watershed is a pre-treatment and must be applied to dry materials or Watershed will not cure and waterproof properly."

I use it often, and like it, but other things work too, for example, Scotchguard, and 303 fabric protector. One interesting thing is that you can Pre-treat tying materials, before tying the flies too.

I used this product a number of years ago. It is not an end all for floating a fly. I still end up using a float. But I figure the two together help.

I also have used a product called Hydrostop by Loon. I think that it works a little better than the water shed. It is more convenient to use as it comes in a small wide mouth container. I drop the flies into it and let them soak then take them out and let them sit in the lid to drain off the excess.

After either one is slimmed you need something to help get the fly to floating again.

I gave it a good trial a few years back and didn't notice much difference between pre- treated and regular patterns when it came to keepin them floating on the stream . I ended up needing the same amount of dessicant and/or floatant with both groups so I stopped using the stuff. Same with scotchgard......fwiw