Freestone · Mixed · Colorado, US

St. Vrain Creek (Lyons)

St. Vrain Creek (Lyons) terrain map

St.

Tomorrow · Not the day for it
Zebra Midge
Forecast · Tomorrow
Not the day for it
Not much stacked in your favour today. Worth an hour if you are nearby, not worth the special trip.
45% projected
Today's fly
Zebra Midge
Zebra Midge
Conditions on the water · Tomorrow
Estimate
Level
Dry recently
No gauge reading
Water temp14.9°C
ClarityUnfishable
Weather20°C
WindN 13 km/h
Pressure1012 hPa
Rain · recent0.3 mm
Rain · ahead0.0 mm

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

Water temperature for Brown Trout
Ideal
15°C est.ideal 10–16°C
0°14°28°
How to fish it · for Brown 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
Excellent — water temperature is right today, though river flow could be better.
Likely species
Mayflies
Caddisflies
Hatch timeline · tomorrowPeak at 11am

12pm(now) — Reed Smut

Stage: On emergersApproach: Emerger or dryActivity: 40%
Also:Trico30%Flying Ants29%
Peak emergence window5 food groups active

Peak activity at 11am — Reed Smut (Reed Smut, Peak emergence window)

Sub-surface · on the nymphunder the surface

Hatch predictions

Top nymph shown — see all 2 guilds with Pro.

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Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

Top prey shown — see all 2 with Pro.

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Evidence
Records-basedModerate confidence

Based on species-occurrence records, not local invertebrate surveys.

Through the year
0–3 scale · September 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
Brown DunHatch
2
3
3
3
3
3
3
2
Western Green DrakeHatch
2
2
Flav (Small Western Green Drake)Hatch
2
3
2
Mahogany DunHatch
2
2

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

Ranked for today
Brown Trout fly box
SD
Sex Dungeon
2-6 · Pattern
Proven pattern for this period
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
Other water nearby · 4
Big Thompson River (canyon, below Lake Estes)
22 km
Brown trout · Rainbow trout
Boulder Creek (Boulder Canyon)
25 km
Brown trout · Rainbow trout
Cache la Poudre River
49 km
30
Brown trout · Rainbow trout
Clear Creek (Golden)
52 km
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 Brown Trout · confidence 90%
How the 80 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow60 × 22%13.2
Clarity95 × 18%17.1
Feeding Time65 × 13%8.5
Pressure80 × 7%5.6
Insect activity61 × 12%7.3
Conditions total= 80
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitymodelled from regional profilemodelled
What would change the calculation
The dawn and dusk windows score higher than the midday lull.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout 1 January → 31 December
Related guides
Euro Nymphingsubsurface methods
Booking & contacts