I spent about 6 hours yesterday above the bridge and below the dam.
It was one of those Putah Days with fish jumping out of the water while chasing something and with big fish below chasing something.
The something wasn't what I offered from standard little Putah Creek flies to terrestials to pupahs to intemediates to egg flies to dry flies to beadhead PT's.
About every October, I have a few of these days at Putah. There is no obvious hatch and the more immature fish are breaking through the surface while after some intermediate something.
One of the less friendly fishers watched me and others from up high with his binoculars. He admitted under duress/questioning in the parking lot that he didn't see anything he recognized as targets for the fish. He and another grand father said the fish appeared to be feeding on small white to opaque things flowing down stream. 2 years ago, I observed the same feeding frenzy on what appeared to be small white to opaque balls about 1 to 2 feet below the surface.
Even the worm, salmon egg, corn and trout food fishers had no luck. I saw one small 10 inch hatchery trout taken on a spinner.
This was my first trip to Putah since the dire warnings of the snail. In spite of the dire warnings, there was ample moss on the rocks, weed growth and green stuff floating down stream. The big fish were there as well as 1 to 2 year fish.
I shall return next week. If you see an old Grampa with a 12' Spey Rod, stop and say hi. If I'm catching anything, I will tell you what is working and not working.
I will try to make it out on Sun, or Fri, good, luck when you head out, I saw the same thing you are talking about, the small fish jumping and all that in Canada this summer, and we could not really figure figure it out at all, the only notable thing was it was right before a huge sedge hatch up there. good luck, if you can figure it out, let us know.
Grampa Spey...Thanks for your report. Yup, getting skunked is part of the fishing "journey". I'm curious about your spey outfit. What gear are you using and does the "tightness" of the creek affect your overall spey casting? Thanks. TMS
I use it above the bridge and with the newer Rio Skagit 450 line, I can use a floating tip, a sinking tip or I can attach an indicator rig. The Skagit line allows one to spey cast without any backcast room. There are many areas above the bridge that are excellent for the small spey rods. Down stream, there are a few areas for using streamers with a spey rod and a Skagit line where it would be impossible to use a one handed rod.
There are areas where you can't use a rod of this length. In those areas I use Bob Meiser's 10' 6" two handed switch 5/6 rod. It really isn't a spey rod but the two hands enable incredible line control, roll casting and switch casting. The rod is a high sticker's dream in tight quarters.
3 years ago I tore my rotator cuff and my bicep head, and I'm not able to use a one handed rod any more. This year, I tore my right bicep in May and thanks to physical therapy, I can use my two handed rods again. I bought the Sage 5120 to use during rehab and to fish the smaller streams and rivers. It is a truly awesome little rod.
In the past I have successfully used the Sage 7136 and 6126 in Putah Creek areas where spey casting can be done or high sticking with an indicator and a spey rod. The 5120 seems capable of doing what these heavier rods can do with less wear and tear on an old body. The 5120 is shorter and can be used in tighter areas.
Last but not least, I can spey cast in Putah Creek after about a 40 minute drive instead of a 3 to 8 hour drive.
In spite of the dire warnings, there was ample moss on the rocks, weed growth and green stuff floating down stream. The big fish were there as well as 1 to 2 year fish. 
and thanks to physical therapy, I can use my two handed rods again. I bought the Sage 5120 to use during rehab and to fish the smaller streams and rivers. It is a truly awesome little rod. 