Seasonal Fly Selections for Rainbow Trout in Colorado: Matching the Hatch All Year Long

Fly fishing in Colorado offers year-round opportunities, and knowing how to match the hatch is essential to consistently catching rainbow trout. Each season brings different insect activity, and having the right flies in your box is critical to success. Let’s break down the best flies and techniques to use for rainbow trout across the seasons.

Spring (March - May)

As snowmelt begins, the water levels rise and temperatures start to increase. This triggers a variety of hatches, including blue-winged olives (BWOs) and midges. Nymphing with small flies is often your best bet during these months, as the water is still relatively cold, and trout are feeding below the surface.

• Best Flies:
  • Pheasant Tail Nymphs (Sizes 16-20)
  • Parachute Adams (Sizes 16-22) for surface action
  • Blue-Winged Olive Emergers (Sizes 18-22)​

Summer (June - August)

Summer brings an explosion of insect life, and trout are more likely to feed on the surface. The famous Green Drake hatch begins in mid-summer, offering some of the best dry fly fishing of the year. Additionally, PMDs (Pale Morning Duns) and caddisflies are in abundance. Dry-dropper rigs work well during this time, especially in the slower-moving sections of rivers.

• Best Flies:
  • Elk Hair Caddis (Sizes 14-18) for caddis hatches
  • Green Drake Dry Flies (Sizes 10-12) during peak hatch
    Pale Morning Dun (Sizes 16-18) for morning fishing​(
     

Fall (September - November)

As water temperatures cool, blue-winged olives make a return, and tricos start hatching. The trout are active but tend to feed more conservatively as winter approaches. Nymphing continues to be effective, but dry flies still work well on warmer fall days.

• Best Flies:
  • Trico Spinner (Sizes 20-24)
  • Zebra Midge (Sizes 18-22)
  • Parachute Adams (Sizes 18-22)​

Winter (December - February)

Winter fly fishing in Colorado can be productive, especially on tailwaters where the water remains relatively warm. Midges are the primary food source, so small nymphs and emergers will be your go-to flies.

• Best Flies:
  • Rainbow Warrior (Sizes 18-22) for nymphing
  • Griffith's Gnat (Sizes 18-22) for dry fly action on mild days
  • Mysis Shrimp (Sizes 16-18), especially near dams​

Match the Hatch Year-Round

By adjusting your fly selections based on seasonal insect activity, you can increase your chances of success when targeting rainbow trout in Colorado. Whether you're nymphing in winter or casting dry flies during a summer hatch, the key is understanding what the trout are feeding on at any given time.