The Masking Hatch…. If you are fishing the Metolius this time of year, this is a term you need to know. I was first introduced the term in 1986 when I was working at the Fly Box in Bend and the iconic 3M Scientific Anglers Strategies for Selective Trout and Advanced Strategies for Selective Trout VHS tapes were delivered to the shop. https://scientificanglers.com/strategies-for-selective-trout-with-doug-swisher/
Doug Swisher was the man of the hour in those videos and I watched them over and over and over learning how to become a better spring creek angler. In one segment, he was fishing a Montana river while there were multiple hatches occurring and was explaining how the fish would be keyed on to just one of the hatches and in that video he named what he saw the “masking hatch”. 
Sometimes the most obvious or prevalent insect is hiding (or masking) the hatch that the fish are actually eating. Not always, but pay attention to the possibility of that and change flies accordingly. 
Last evening on the Metolius this was a lesson to be revisited and I’ll share the story now. Chester and I arrived just after work to the Wizard Falls area and walked downstream to the Dolly Hole where a whole bunch of hatches were occurring at the same time. Caddis, Stoneflies, Mayflies. The most obvious ones were PMD’s, the yellow sailboats were easy to identify. Seemingly tens of thousands Little Olive Stones were in the air so it was easy to assume some of the bugs would also be on the water too, and the sippy rises would indicate fish could be eating them. There were also some gorgeous cinnamon colored #16 caddis mixed in, and that caught my eye but I didn’t think the fish were eating those due to the rise forms being so gentle. 
I started with a PMD and got a sip on the 1st cast of the night. Then nothing. And nothing. In fact the fish spooked from the refusal and never rose again. So I moved 50 feet upstream and found 2 more rising fish. I switched the fly to a Henryville that I clipped all the hackle from the bottom to achieve a lower float profile and put it over both fish with a number of good drifts and never had a look. As luck would have it, one of my customers came up river, and stopped to say hello and he said he had just caught a nice fish on a BWO Film Critic downriver. In the glare of the smokey evening, I never noticed the BWO’s but knew they are certainly part of the early evening hatch cycle this time of year so I took my queue and clipped off the Henryville and tied on the BWO. 2 or 3 casts later we were landing the 1st fish of the night. “Masked” or not, it is important on the Metolius (and many other waters) to change flies. 
How many fly changes you ask? I have counted flies on my foam patch after a fishing session on the Met and going through over 10 fly changes is not uncommon. Sometimes 14, 15 or more. Ask how many hatches are occurring in the hours you’ll fish? What stage are the fish keyed in on? Is it: Emergers? Cripples? Duns? Spents? Midges? Stones? Mayflies? Caddis? Terrestrials? Think about those options when you open your box and if you’ve worked a fish with a good fly with several good drifts change flies. 
If fish are refusing a fly, I’d add lighter tippet 1st and keep the fly to see if that is the difference maker. 
Chester said last night as we were walking the mile back to the truck in the dark how dry fly fishing on that river is so addicting, filled with anticipation, disappointment, and occasional achievements. If it were simple it would not be nearly as fun. This is why we love this river.

The Metolius River Report is largely in my opening comments, but there is more to tell. Much more, as that captured a moment of evening fishing in a short segment of the river. Starting up near the Tract C Bridge and down to the Canyon you’re going to be running in to Goldenstone Adults and PMD’s, Caddis, Little Olive Stones, Mahogany Duns and a lot of good Euro Nymphing water too. 
From the Canyon to below Bridge 99 is where the Green Drakes #10 and Flav’s #14 will be found. This is a very important afternoon hatch for the next few weeks and will be found at some point between 1 and 5 most days. 
Mahogany Duns #16, PMD’s #16, BWO’s #18-20, Tan Caddis #16, Grey Caddis #14, Yellow Caddis #18, October Caddis #8 (pupa mostly), Cascade Stone #4-6, Rusty Spinners #16, Olive Spinners #20 are all hatches you will run in to in the middle and lower river stretches from Canyon Creek to Candle Creek. 
Bull Trout Fishing is good. It is the time of the year to fish the biggest streamers if you want, but don’t forget the Euro Jig Streamers like a Sir Mix A Lot and Busta Seams are great flies Euro rigged or under the bobber. 
Euro Nymphs, TJ Hookers, 20 inchers, Caddis Pupa, Brown or Olive Mayfly Nymphs and Stonefly Nymphs (black and golden) are great nymphs for the season.