in a river 30 minutes drive, that fresh water crab is the only thing the trout will eat. Mayflie and Caddis hatches are not big and frequent enough for them to be real food for the trout, so the trout rarely go surface feeding (but they will take nymphs of these insects and stone fly). Plus there is no good cover, no vegetation, except under the rocks in the bottom, right where the crabs live.
The fly that works OK is a weird hybrid: its a olive and orange woolly bugger with a wing case (!) and three long rubber legs crossing the body in right angles (resulting in 6 perpendicular legs). I tend to think its working more as an attractor fly rather the trout mistaken it for a crab...but I could be wrong.
People fish it casted upstream, mended upstream for depht, then dead drift with ocasional short and violent strips.