Freestone · Limestone · Alps / Savoie-Isère border

Guiers

A clear mountain stream flowing through the village of Saint-Pierre-dEntremont with alpine peaks behind, on the Guiers river system
Contributor photo

The Guiers Vif at Saint-Pierre-d'Entremont, on the Savoie–Isère border

Florian Pépellin

1st-category river on the Savoie-Isère border with ~1.

Poor · Brown Trout
Small Perdigón · 16-20
Poorlive now
Not the day for it
River temperature is the limiting factor today, not the flow. This is not the day to push it. Check the thermal advice above before you head out.
90% confidence
What moved it
  • LevelDry recentlyNo gauge reading
  • Water temp22.1°C
  • ClarityClear
Today’s fly
Small Perdigón
Small Perdigón16-20
Euro-nymph
Conditions on the water
Estimate
Level
Dry recently
No gauge reading
Water temp22.1°C
ClarityClear
Weather23°C
WindS 4 km/h
Pressure1017 hPa
Rain · recent0.2 mm
Rain · ahead25.4 mm

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

Water temperature for brown trout
Warm — slow
22°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
⛔ 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
Survey-backed · regionalModerate confidence

Backed by regional invertebrate surveys; no sampling on this exact reach 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
1
Grayling seasonSeason
1
2
2
2
1
Alpine RhithrogenaHatch
2
3
3
2
Sculpin / Baitfish (Rivers)Hatch
2
3
3
3
3
3
3
3
2
March BrownHatch
2
3
2
Large StoneflyHatch
2
3
2

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

Ranked for today
Brown Trout fly box
Permits & access
Permit required — see local rules.
  • AAPPMA permits.
What's coming
Plan ahead
5-day outlook
Water here around 22°C. Nothing cooler within range — carry a thermometer.
Gallery · 2
  1. A clear mountain stream flowing through the village of Saint-Pierre-dEntremont with alpine peaks behind, on the Guiers river system
    The Guiers Vif at Saint-Pierre-d'Entremont, on the Savoie–Isère border
  2. Terrain map of the venue
    Terrain map
About this water

1st-category river on the Savoie-Isère border with ~1.5 km no-kill course through limestone and alpine terrain where geology changes hands. Selective dry-fly water in pristine conditions. Spring through early autumn offers consistent fishing. Mountain character with responsive flow. Some sections may have specific regulations; verify with local AAPPMA.

  • Limestone
Water quality (WFD)
  • Ecology: Moderate
  • Chemical: Unknown
What this classification means

WFD ecological status Poor → Moderate corrected to EEA WISE 2022 (3rd RBMP) classification for waterbody FRDR515 (was a stale earlier-cycle value). Source: EEA WISE SWB_SurfaceWaterBody (discodata.eea.europa.eu), verified 2026-06-18.

WFD classification · FRDR515

The full read · show the working · for brown trout · confidence 90%
How the 12 is built — score × weight = contribution
Temperature6 × 28%1.7
Flow60 × 22%13.2
Clarity95 × 18%17.1
Feeding Time40 × 13%5.2
Pressure80 × 7%5.6
Insect activity52 × 12%6.2
Limiting factor: Water temperature (22.1°C) is outside Brown Trout's preferred range (10–16°C)= 49
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitysurvey-backed invertebrate datasurvey
What would change the calculation
Cooler water — back toward the 10–16 °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
  • Trout2nd Saturday of March → 3rd Sunday of September
  • Grayling3rd Saturday of May → 3rd Sunday of September

    France national rule: grayling opens 3rd Saturday of May in all waters. In 1st category (salmonid) rivers, grayling closes with the trout season on the 3rd Sunday of September. Departmental regulations may impose additional restrictions. Always check the relevant département's 2026 arrêté préfectoral.

Related guides
Grayling Playbookgrayling tacticsPyrenees PlaybookFrench riversEuro Nymphingsubsurface methods
Booking & contacts