Brown trout like this are taking spruce moths and large fluttering caddis. Size 10-12 Elk Hair Caddis or Stimulators will do the job:
Rainbow trout tend not to be so selective, feeding on the smaller caddis (I like #16 or even 18 Goddards) as well as larger bugs. Also, as the sun gets high and the brown trout action tapers off, the (generally smaller) rainbows still feed greedily:
I'm the first to recognize it and my fishing friends will attest to the fact that I am a mediocre caster. I overcome this, in part, by using a leader of 11+ feet including a 5X or even 6X tippet of 2 feet or so--this allows for lots of slack near the fly, and hence a more drag-free drift of the fly. Keeping hooks VERY sharp (I carry a little diamond stick) also helps make your fly "sticky."
While fishing, be sure to look up once in awhile. Otters, mink, beaver, and other wildlife such as pronghorn antelope and mule deer are common where I fish. Here's a mulie fawn with ears nearly as big as it is:
And here's a herd of pronghorn does and fawn feeding in a hayfield near the river:
Sadly, MollyTheDog is out of action for a few weeks when it comes to fishing or hiking. She cut her foot badly while running behind our house--requiring stitches and a cumbersome bandage. Sad puppy:
Like any river, if you're new to the Big Hole you probably need some guidance. Stop in and see Al Lefor at Great Divide Outfitters near "Silver Bridge"--he'll have the flies & advice you need, and offers guiding service too.
871 Pumphouse Road
Divide, MT 59727