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The tailwater is running low and stable, clarity is excellent, and trout are holding deep in slow winter lanes where they can feed without spending energy. Expect short but meaningful midday feeding windows, especially when sunlight reaches the softer edges. This is Blue River below Green Mountain Reservoir fly fishing in winter: precise, rewarding, and a little unforgiving.
Updated: December 31, 2025
The Blue River below Green Mountain Reservoir is locked into a predictable winter tailwater routine. Flows are steady for the week, water is clear, and most fish are set up in deeper slots, slow inside seams, and soft troughs where they can sip midges without moving far. If you are hoping for aggressive takes, you are on the wrong calendar. If you are willing to fish small, fish slow, and fish accurately, this stretch will still produce.
This week’s update for Blue River fly fishing below Green Mountain Reservoir centers on the same truth you already know but occasionally ignore: depth and drift are everything. Midges are the primary menu item, with mysis showing up as a supporting actor when you put your rig where it needs to be. Keep your profile small, minimize false casts, and treat every run like it has one fish in it. Because it probably does.
Listen to the Audio Overview
Conditions Summary
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Flow: ~350 to 450 CFS below Green Mountain Reservoir, stable early-winter release
Water Temperature: Mid 30s to low 40s
Air Temperature: Mid 20s to upper 30s
Clarity: Very clear
Crowds: Light
Best Window: 11 a.m. to 3 p.m.
Fishing Type Focus: Winter nymphing with small midges and baetis
Weather
Expect cold canyon mornings, pockets of midday sun, and rapid cooling once shadows return. Highs in the upper 20s to high 30s with lows dipping into the teens. Light wind can affect drifts but also encourages midge movement. Midday warmth drives the only consistent feeding window.
Top Flies in Your Box This Week
- Black Beauty 20 to 24
- Zebra Midge (black or red) 20 to 22
- Mercury Midge 20 to 22
- RS2 (black or gray) 20 to 22
- WD-40 20 to 22
- Juju Baetis 20 to 22
- Small Pheasant Tail 18 to 20
- Scud (olive or gray) 14 to 18
Pro Rig of the Week: Green Mountain Deep Slot Rig
- Indicator: Small yarn or minimal pinch indicator
- Lead Fly: WD-40 #22
- Dropper: Mercury Midge #22
- Weight: Add split shot until you tick bottom consistently
- Target Water: Deep troughs, slow inside seams, and winter slots below riffles
Hatch Chart for December
| Bug Type | Size | Notes |
|---|---|---|
| Midges | 20 to 26 | Primary food source; most feeding occurs subsurface |
| Mysis | 14 to 18 | Present in the system; can matter when fish key in deep lanes |
| Winter Stones | 14 to 18 | Limited adult activity; nymphs can be a useful anchor pattern |
Download the Blue River Hatch Chart.
Access Points
Blue River Below Green Mountain Dam ⭐⭐⭐⭐⭐
The premier tailwater stretch with deep seams, canyon structure, and consistent winter flows. Ideal for technical nymphing with small patterns.
Rating: Five gold stars
BLM Access – Canyon Stretch ⭐⭐⭐⭐☆
Mixed pocket water and longer troughs that hold trout during the coldest months. Less pressured than the dam section and excellent for mobile anglers.
Rating: Four gold stars
Confluence Area Downstream ⭐⭐⭐⭐☆
Where the river flattens and widens slightly, offering soft edges and slower winter lanes. Productive on days with light cloud cover.
Rating: Four gold stars
Stop Here After the River
Angry James Brewing Co. (Silverthorne)
A warm, relaxed local brewery perfect after a day in the cold canyon. Expect big mountain vibes, community tables, and comfort-focused après energy.
What to order: The Resolute IPA and the rotating food truck’s signature warm dish.
Local Regulations and Notes
- Watch for changing dam release flows before entering canyon water
- Shelf ice can form along shaded edges
- Wading is technical; use caution on slick canyon rock
- Keep distance from other anglers due to narrow channel geometry
Companion Article
Colorado Winter Trout Feeding Behavior in Clear, Low-Flow Rivers
FAQ
Q: Is the Blue River below Green Mountain Reservoir good in winter?
A: Yes. Stable tailwater flows make it one of the most reliable cold-season fisheries in Colorado.
Q: What flies catch the most fish here?
A: Small midges, baetis nymphs, and subtle emergers are the bread and butter.
Q: Do streamers work?
A: Occasionally. Small leeches can move fish in deep slots on overcast days.
Q: How technical is this section?
A: Very. Clear water and slow current require stealth and precision.
Q: What is the best time of day?
A: Midday, when sunlight and slight temperature bumps activate midges.
Q: Can I sight-fish?
A: Yes in many sections, but trout spook easily in winter clarity.
Q: Is the Blue River below Green Mountain good in winter?
A: Yes. It is one of the most consistent and least crowded winter tailwaters in Colorado.
Q: How technical is this stretch compared to Dillon Dam?
A: Slightly less pressured, but still technical. Depth control and drift quality matter.
Q: Are dry flies an option right now?
A: Rarely. Subsurface midge patterns dominate winter success.
Q: What leader and tippet setup works best?
A: Long leaders with 5X to the lead fly and 6X to the midge dropper.
Q: Do scuds matter here in winter?
A: Yes. Scuds are an important secondary food source in this tailwater.
Q: When does the bite shut down?
A: Typically mid-afternoon once shadows and colder air settle into the canyon.