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Bield:Fish
Hatch profile

Slate Drake

Isonychia bicolor
MayflyEvening12-week run
Water temperature trigger
40°50°60°70°80°
Range: 55–70°F · Peak: 62°F
Fly patterns
  • Slate Drake Parachute #12
  • Iso Comparadun #12
  • Mahogany Spinner #12
  • Iso Nymph #12 (swimming nymph)
Also known as

Iso · Mahogany Dun (spinner)

Long-running hatch from June into October. Nymphs are strong swimmers and crawl out of the water to emerge — fish a swung wet fly through riffles.

Best rivers for the Slate Drake hatch

These rivers list the Slate Drakeas a signature hatch — the local fly shops and angling history confirm it's reliable enough to plan a trip around.

Other rivers with Slate Drake activity

These rivers carry the hatch but at varying intensity — check each river's page for the local peak window.

Get a notification when the Slate Drake is on.

Bield: Fish ties USGS gauge readings to hatch triggers and alerts you when your home river hits the temperature window for the hatch you're waiting on.

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