The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large Brown Trout that only touch streamers for the rest of the year.
It is best fished by casting upstream, allowing it to sink, and then twitching it up through the currents in front of feeding fish.
Time of day: Anytime between noon and dusk, depending on temperature
Habitat: Riffles and rapids
Current speed: Fast
Substrate: Gravel or rock
Environmental tolerance: Very intolerant of pollution or slow water