Big Thompson River
Fly fishing in Colorado · Beginner · Best seasons: Spring, Summer, Fall
Target Species
Rainbow Trout, Brown Trout
About This Water
Flows through scenic Big Thompson Canyon. Both wild and stocked trout with excellent access near Estes Park.
Fishing Recommendations
The Big Thompson River (or "The Big T") is one of Colorado’s most iconic and accessible trout streams. Flowing from the high peaks of Rocky Mountain National Park (RMNP) through the dramatic Big Thompson Canyon and down into the city of Loveland, it offers a diverse range of water types—from meandering meadow streams to high-gradient pocket water.
Here is your comprehensive guide to fly fishing the Big Thompson.
🎣 Location Overview
The Big Thompson is a tale of two rivers.
- The Upper River (RMNP): Inside the park, specifically in Moraine Park and Forest Canyon, the river meanders through lush meadows. It is classic small-stream fishing where stealth is rewarded.
- The Canyon (Below Lake Estes): This is the most famous stretch. It is a high-gradient, boulder-strewn canyon that parallels Highway 34. The stretch immediately below Olympus Dam is a "tailwater" section that stays ice-free in winter, while the rest of the canyon fishes like a classic freestone.
What makes it special: Its accessibility and "fishiness." You can park your car and be casting into prime pocket water within thirty seconds. The scenery is world-class, and the biomass of fish per mile is exceptionally high.
🐟 Target Species & Behavior
- Brown Trout: The dominant species in the canyon. They are opportunistic but wary. In the canyon, they hold in the "cushion" in front of boulders, in deep plunge pools, and along the soft edges of fast current.
- Rainbow Trout: Found throughout the river, but heavily concentrated in the catch-and-release sections. They tend to hold in the faster riffles and the heads of pools.
- Behavior: During hatches, these fish are incredibly surface-oriented. In the meadow sections of RMNP, they are spooky; in the canyon, they are less worried about your presence and more focused on the fast-moving current.
📅 Best Times to Fish
- Spring (March - May): The tailwater section below the dam is excellent in early spring. Look for Midges and Blue Winged Olives (BWO). Be wary of runoff in late May, which can turn the river high and murky.
- Summer (Late June - August): The "Golden Age" of the Big T. Flows stabilize, and the dry fly fishing is spectacular. This is prime time for Caddis, Pale Morning Duns (PMDs), and Terrestrials.
- Fall (September - November): My personal favorite. The Brown trout become aggressive as they prepare to spawn. The crowds thin out, and the BWO hatches return. The "walk-wade" conditions are perfect as water levels drop.
- Best Time of Day: In mid-summer, get there at dawn to beat the heat and the crowds. In spring and fall, the 10:00 AM to 3:00 PM window is most productive as the water warms.
🪰 Recommended Flies & Techniques
Top Fly Patterns
- Dry Flies: Elk Hair Caddis (size 14-18), Amy’s Ant (size 12-14), Parachute Adams (size 16-22), Hippie Stomper (size 14-16), and Stimulators.
- Nymphs: Pat’s Rubber Legs (size 10-12), Pheasant Tail (size 16-20), Zebra Midge (size 18-22), RS2 (size 18-22), and Two-Bit Hookers.
- Streamers: Black or Olive Wooly Buggers and Sparkle Minnows (fish these deep in the plunge pools).
Effective Techniques
- Dry-Dropper: The gold standard for the Big T. Use a buoyant dry fly (like a Chubby Chernobyl or Stimulator) and hang a small nymph 18-24 inches below it. This allows you to cover two zones in the pocket water without a bobber splashing down.
- Tight-Line/Euro Nymphing: Because the canyon is full of complex currents, a traditional indicator often creates drag. Tight-lining through the deep slots is incredibly effective here.
- The "Meadow Stealth": In RMNP, stay low, wear drab colors, and keep your shadow off the water.
💡 Pro Tips & Local Knowledge
- Read the "Cushion": In the canyon, beginners often fish the "tail-outs" of pools. Pros fish the front of the boulders. There is a pocket of soft water right in front of a rock where the current splits—big Browns love to sit there and wait for food.
- Don't Overlook the "Skinny" Water: People often walk past water that is only 6-12 inches deep. On the Big T, if there is a rock providing a break in the current, there is likely a trout behind it.
- The "Below the Dam" Secret: The first mile below Olympus Dam is technically a tailwater. Even if the rest of the canyon is blown out or frozen, this section remains fishable. It is highly technical—use 6x or 7x tippet and tiny flies.
- Estes Park Crowds: During the summer, the river through the town of Estes Park is heavily pressured. Drive 15 minutes down the canyon to find more "wild" fish.
⚠️ Important Information
- Regulations: Regulations change frequently. As of current standards, the section from Olympus Dam to the Waltonia Bridge is Catch and Release only and restricted to artificial flies and lures. Always check the current Colorado Parks and Wildlife (CPW) brochure.
- Access: Much of the canyon is public (US Forest Service), but there are pockets of private land clearly marked with signs. Please respect "No Trespassing" signs.
- Park Entry: To fish the upper river in Rocky Mountain National Park, you will need a Park Pass and, during peak season, a Timed Entry Permit.
- Safety: Highway 34 is narrow and busy. Park only in designated pull-outs and be extremely careful crossing the road. The rocks in the river are notoriously slippery—felt soles or studs are highly recommended.
Bug Hatches & Matching Flies
| Hatch | Type | Peak months | Time of day | Hook sizes | Matching flies |
|---|---|---|---|---|---|
| Midges Chironomidae | midge | January, February, March, November, December | Late Morning/Afternoon | #18-24 | Zebra Midge #18-22, Griffith's Gnat #20-24, Top Secret Midge #20-22 |
| Blue Winged Olive Baetis | mayfly | March, April, September, October | Late Morning/Cloudy Afternoons | #18-22 | RS2 #20-22, JujuBaetis #18-22, Parachute Adams #18-22 |
| Pale Morning Dun Ephemerella | mayfly | June, July, August | Mid-Morning/Early Afternoon | #16-18 | PMD Sparkle Dun #16-18, Pheasant Tail #16-18, Barr's PMD Emerger #16-18 |
| Mother's Day Caddis Brachycentrus | caddis | May | Afternoon/Evening | #14-16 | Elk Hair Caddis #14-16, LaFontaine's Deep Sparkle Pupa #14-16, Peacock Caddis #16 |
| Spotted Sedge Hydropsyche | caddis | June, July, August, September | Evening | #14-18 | Puterbaugh's Foam Caddis #16-18, Graphic Caddis #16-18, Holy Grail #14-16 |
| Golden Stonefly Hesperoperla pacifica | stonefly | June, July | Morning/Afternoon | #8-12 | Pat's Rubber Leg #8-12, Amy's Ant #10-12, 20 Incher #10-14 |
| Trico Tricorythodes | mayfly | August, September | Early Morning | #20-24 | Trico Spinner #20-24, Sunken Trico #20-22, Drowned Trico #22-24 |
| Terrestrials Various | terrestrial | July, August, September | Mid-day/Afternoon | #10-18 | Hopper Juan #10-14, Cinnamon Ant #16-18, Black Beetle #14-16 |
| Red Quill Rhithrogena | mayfly | May, June | Afternoon | #12-14 | Red Quill #12-14, Hare's Ear #12-14, Quill Gordon #14 |