Actually, I do have one fly I've caught fish in both summer and winter. But I mostly fished the stained rivers of the OP, which even in summer months stays somewhat stained (but does clear up). I've used my old trusty pink bunny leech. I actually tried it by accident. Was taking a girlfriend around the "Loop" back in about 86'. We were camping at Minnie near end of the trip (started on Eastside and worked up and around to westside). Well, didn't bring any gear with me. Was supposed to be a fun "romantic" rustic style weekend. It was actually. But, I had a serious itch going over all these rivers I normally fished back then and couldn't fish. I was out scouting the spot near Willoughby, and remembered I had a rod stashed in the back of my Blazer (I had a locking compartment in my old Blazer I had on the passenger side of truck over wheelwell). I had my 8wt outfit and a box of winterflies. The pink leech was the smallest profile I had (yes, I used some gawdy flies then). Sure enough, I landed 3 nice summerruns in about an hours time (it was early morning and she was still sleeping). Fishing was good, but had to get back to camp before she woke up. From then on, I always kept a few on hand. Luckily, I didn't get caught. Was a condition I didn't fish. LOL. Had to wash up extra hard to get the smell off my hands of the fish. But, was worth it.
"Good angling ethic is not a monopoly practiced just by fly fisherman" - Bill McMillan