Dry fly
Isonychia
Fast-water dark dun (Slate Drake)
TroutSurface
A big, dark, fast-water mayfly — Isonychia, the Slate Drake — with a mahogany-and-slate body and a habit of crawling to the banks to emerge. It hatches sporadically from late spring into autumn, and a big dark dun drifting over a riffle pulls the better fish up.
Fish this when
Late spring through autumn on eastern and midwestern freestone rivers, often a sporadic afternoon-into-evening emergence. Fish a size 10–12 dark dun through riffles and runs; a nymph swung to the bank covers the crawling emergers.
Why it works
Isonychia are large, agile-swimming mayflies that emerge near the banks, so a substantial dark dun over fast water is a big, worthwhile mouthful trout will move for even outside a heavy hatch.
Naturals it imitates
Isonychia dun — large dark slate-bodied mayfly
Typical zone & fishable range
usually
Surface
Film
Subsurface
Deep
Setup sensitivity: medium
Quick facts
Tying difficulty
Intermediate