Mastering Fly Selection for Trout in Colorado

Fly fishing for trout in Colorado is an art steeped in observation, strategy, and adaptability. With the state’s diverse waters—from freestone rivers to tailwaters and spring creeks—anglers are presented with endless opportunities and challenges. One of the most critical aspects of fly fishing is selecting the right fly. A thoughtful approach to fly selection can turn a good day into a great one.

In this blog, we’ll dive deep into the factors that influence fly selection for trout in Colorado. From understanding bug species and their life cycles to recognizing where trout feed in the water column, we’ll also explore how to rig your fly for a natural presentation.

1. Types of Bugs Trout Feed On

Colorado’s rivers, streams, and lakes are teeming with aquatic insects that form the backbone of a trout’s diet. Understanding these insects and their life cycles will help you choose the right fly to match what trout are eating. Here are the key insect groups you should know:

Mayflies

• Life Cycle: Nymph → Emerger → Adult (Dun) → Spent (Spinner).

• When to Use: Year-round but especially during prolific hatches in spring and fall.

• Popular Patterns: Blue-Winged Olive, Parachute Adams, Rusty Spinner.

• Tips: Mayflies are delicate and require subtle presentations. Match the hatch closely in size and color for success.

Caddisflies

• Life Cycle: Larva → Pupa → Adult.

• When to Use: Late spring through early fall, with evening hatches being particularly productive.

• Popular Patterns: Elk Hair Caddis, LaFontaine’s Sparkle Pupa, X-Caddis.

• Tips: When fishing caddisflies, focus on riffles and fast-moving water where they emerge and lay eggs.

Stoneflies

• Life Cycle: Nymph → Adult.

• When to Use: Late spring to early summer during large stonefly hatches.

• Popular Patterns: Stimulator, Pat’s Rubber Legs, Golden Stone Nymph.

• Tips: Stoneflies are large and often trigger aggressive strikes. Use them in fast runs and pocket water.

Midges

• Life Cycle: Larva → Pupa → Adult.

• When to Use: Year-round, especially in winter when other insects are less active.

• Popular Patterns: Zebra Midge, Griffith’s Gnat, WD-40.

• Tips: Midges are small, so use light tippets (6X or 7X) and focus on slower water where trout feed deliberately.

Terrestrials

• Examples: Grasshoppers, ants, beetles.

• When to Use: Late summer when terrestrial insects are blown into the water.

• Popular Patterns: Chubby Chernobyl, Dave’s Hopper, Ant Patterns.

• Tips: Use terrestrials along grassy banks and in windy conditions for the best results.

2. Reading the Water Column

Trout feed in different parts of the water column depending on the conditions and the insects available. Learning to recognize these feeding zones is essential for fly selection and presentation.

Surface Feeding

• Signs: Trout rising or sipping flies from the surface.

• Fly Selection: Dry flies or emergers. Match the size and color of the insect trout are feeding on.

• Presentation: Cast upstream and let the fly drift naturally. Focus on achieving a drag-free drift to mimic the behavior of real insects.

Subsurface (Mid-Column) Feeding

• Signs: No surface activity, but trout are flashing or holding just under the surface.

• Fly Selection: Emergers, unweighted nymphs, or soft hackles.

• Presentation: Use an indicator rig or tight-line nymphing to keep flies at the desired depth.

Bottom Feeding

• Signs: Trout holding deep in runs or pools, often visible with polarized glasses.

• Fly Selection: Weighted nymphs or split-shot rigs. Use flies like Pheasant Tails, Pat’s Rubber Legs, or stonefly nymphs.

• Presentation: Get flies down quickly with tungsten beads or added weight. Ensure your fly ticks the bottom occasionally to stay in the feeding zone.

3. Rigging for Natural Presentation

Even the most realistic fly won’t fool a trout if it doesn’t behave naturally. Rigging your fly to mimic the behavior of the insects trout are feeding on is crucial. Here’s how to do it:

Dry Fly Rigs

• Use a tapered leader (9-12 feet) to allow for delicate casts.

• Attach a tippet (5X or 6X) for a more subtle presentation.

• Cast upstream and focus on achieving a drag-free drift by mending your line and avoiding tension on the fly.

Nymph Rigs

• Set up a two-fly rig with a weighted nymph as the point fly and an unweighted fly as the dropper.

• Use an indicator to suspend the flies and adjust it to match the depth of the water column.

• Ensure the flies drift naturally by keeping the indicator moving at the same speed as the current.

Streamer Rigs

• Use a shorter leader (4-6 feet) to keep the fly deeper in the water.

• Attach your streamer with a loop knot to allow for more realistic movement.

• Vary your retrieves—long and slow strips mimic injured baitfish, while quick strips imitate fleeing prey.

Dry-Dropper Rigs

• Combine a buoyant dry fly with a subsurface nymph or emerger.

• Tie the nymph off the bend of the dry fly hook with a short length of tippet (12-18 inches).

• This rig is excellent for covering both surface and subsurface feeders.

4. Key Factors in Fly Selection

Fly selection isn’t just about matching the hatch—it’s about understanding the details that make a fly effective. Here are the main factors to consider:

Shape

• The silhouette of your fly should closely resemble the insect it’s imitating. Mayflies have a slim profile, while caddisflies are bulkier.

Color

• Match the color of the natural insect as closely as possible. Use lighter colors in clear water and darker colors in stained water.

Size

• Trout are often keyed into specific sizes, especially during hatches. Carry a range of sizes to adjust to what the fish are eating.

Weight

• Use weighted flies or add split shot to get nymphs and streamers down to the feeding zone. Tungsten beads are a great option for fast currents or deep pools.

Action

• The way a fly moves in the water is critical for streamers and certain nymphs. Consider the retrieve speed or the fly’s inherent movement (e.g., soft hackle flies have natural movement in the current).

5. Colorado-Specific Fly Recommendations

Colorado’s rivers, streams, and lakes host an array of insects, and having the right flies in your box is essential. Here are some proven patterns for fishing in the Centennial State:

Spring

• Blue-Winged Olive (sizes 18-22).

• Pheasant Tail Nymph (sizes 16-20).

• Zebra Midge (sizes 18-22).

Summer

• Elk Hair Caddis (sizes 14-18).

• Chubby Chernobyl (sizes 10-14).

• Parachute Adams (sizes 14-18).

Fall

• Rusty Spinner (sizes 18-22).

• Hare’s Ear Nymph (sizes 16-20).

• Pat’s Rubber Legs (sizes 8-12).

Winter

• Griffith’s Gnat (sizes 20-24).

• WD-40 (sizes 20-24).

• RS2 (sizes 20-24).

A Day on the Water: Putting It All Together

Imagine it’s a crisp fall morning, and you’re fishing the South Platte River below Cheesman Canyon. The water is clear, and the temperature hovers around 50°F—perfect conditions for trout activity. You observe the water and notice a few fish rising in a slow-moving seam.

You start with a dry-dropper rig, tying on a size 16 Parachute Adams with a size 20 Zebra Midge below. Casting upstream, you let the flies drift naturally through the seam. A trout takes the dry fly, and you set the hook, feeling the satisfying pull of a rainbow trout.

As the day progresses and surface activity subsides, you switch to a nymph rig with a Pheasant Tail Nymph and an RS2. You focus on deeper runs and slower pools, adjusting your indicator to match the depth. The subtle movement of your indicator signals another strike, and the day continues with success.

Final Thoughts

Fly selection is an art that combines observation, knowledge, and creativity. By understanding the insects in Colorado’s waters, reading the trout’s behavior in the water column, and rigging your flies for natural presentations, you’ll improve your chances of success and deepen your appreciation for the sport.

Remember, fly fishing is about more than catching fish—it’s about connecting with nature, learning from every cast, and enjoying the process. Colorado’s rivers and trout offer endless opportunities to grow as an angler. So take the time to observe, experiment, and have fun.

“-Until next time—fly fish your water, your way.”

JRO