Freestone · Mixed · Colorado

St. Vrain Creek (Lyons)

St. Vrain Creek (Lyons) terrain map

St.

Poor · Rainbow Trout
Parachute Adams · 12-18
Poorlive now
Not the day for it
Low and clear — careful approach country. A morning for the obvious fish only.
90% confidence
What moved it
  • LevelDry recentlyNo gauge reading
  • Water temp22.1°C
  • ClarityClear
Today's fly
Parachute Adams
Parachute Adams12-18
High-confidence seasonal pick
Conditions on the water
Estimate
Level
Dry recently
No gauge reading
Water temp22.1°C
ClarityClear
Weather24°C
WindE 10 km/h
Pressure1015 hPa
Rain · recent0.0 mm
Rain · ahead1.4 mm

No gauge on this water — readings are regional estimates from weather, not a live gauge.

Water temperature for Rainbow Trout
Warm — slow
22°C est.ideal 10–18°C
0°14°28°
How to fish it · for Rainbow Trout
When
Nymphing can work through most of the day.
Where
Cover mixed depths.
Method
Start with tight-line nymphs and adjust if fish rise or drift higher.
Kit
9 ft #4 rod, floating line, 12 ft tapered leader to 4–5 lb fluoro tippet.
Why this works
Water at 22.1°C. This is the line where catch-and-release kills brown trout. Do not fish for them today.
Hatch timeline · todayQuiet day

Hatch predictions

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Sub-surface · on the nymphunder the surface

Hatch predictions

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Beyond the hatch · worth watchingambient prey

Hatch predictions

Top prey shown — see all 2 with Pro.

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Evidence
ModelledModerate confidence

Modelled from regional ecology — no survey or occurrence data for this water yet.

Through the year
0–3 scale · July highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
2
2
2
2
2
1
Western Green DrakeHatch
2
2
Flav (Small Western Green Drake)Hatch
2
3
2
Mahogany DunHatch
2
2
American March BrownHatch
2
3
2

Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.

Ranked for today
Rainbow Trout fly box
Permits & access
Permit required — see local rules.
  • Colorado licence
  • Verify CPW rules
  • Town/park access at Lyons; USFS access in the upper canyon forks.
What's coming
Plan ahead
5-day outlook
Cooler water nearby · 1
Probably above the Rainbow Trout safety line — these are likely cooler, but carry a thermometer.
Big Thompson River (canyon, below Lake Estes)
22 km
~10°C
Brown trout · Rainbow trout
About this water

St. Vrain Creek comes down two canyon forks to meet at Lyons, a small Front Range freestone that took the brunt of the 2013 flood and has come back as honest brown-and-rainbow water. The town and park reaches around Lyons are easy and accessible; the North and South St. Vrain canyons above offer more pocket water and fewer people for the price of a little walking. It's classic local quick-hit fishing — not a destination, but a friendly, fishable creek a short hop from Boulder and Longmont, best after the spring runoff settles.

  • Mixed
Water quality · US Clean Water Act
  • Aquatic life: Supporting
  • Recreation: Impaired
What this classification means

Recreation: Bacteria/pathogen advisory — mind wading cuts and immersion.

EPA ATTAINS assessment unit 'St. Vrain Creek, mainstem' (COSPSV03_D), 2024 Integrated Report. Aquatic Life use: Fully Supporting. Listed impairment causes: Pathogens. This is a Clean Water Act assessment-unit classification (the US analogue of WFD), not a live reading.

Status is for the Clean Water Act assessment unit covering this reach.

EPA ATTAINS (Clean Water Act) · COSPSV03_D

The full read · show the working · for Rainbow Trout · confidence 90%
How the 15 is built — score × weight = contribution
Temperature10 × 28%2.8
Flow80 × 22%17.6
Clarity85 × 18%15.3
Feeding Time55 × 13%7.2
Pressure75 × 7%5.3
Insect activity49 × 12%5.9
Limiting factor: Water temperature (22.1°C) is outside Rainbow Trout's preferred range (10–18°C)= 54
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitymodelled from regional profilemodelled
What would change the calculation
Cooler water — back toward the 10–18 °C ideal band — would lift the score and ease welfare.
The dawn and dusk windows score higher than the midday lull.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout1 January → 31 December
Related guides
Euro Nymphingsubsurface methods
Booking & contacts