Freestone · Mixed · Wallonia / Luxembourg Province, BE

Semois

Semois — File:Frahan JPG01.jpg
Marginal · Brown Trout
Pheasant Tail Nymph · 14-18
Marginallive now
Slow going — pick your moments
River temperature is the limiting factor today, not the flow. Fish dawn or dusk if you go at all, and handle everything with extra care.
80% confidence
What moved it
  • Level0.01 mDropping after lift
  • Water temp19.6°C
  • ClarityVery colouredColouring up
Today's fly
Pheasant Tail Nymph
Pheasant Tail Nymph14-18
Upstream
Conditions on the water
Live gauge
Level
Steady
0.01 m
Dropping after lift
Water temp19.6°C
ClarityVery coloured
Weather21°C
WindE 10 km/h
Pressure1014 hPa
Rain · recent0.0 mm
Rain · ahead4.5 mm

The nearest gauge doesn't record temperatures, so we've estimated it — defer to the river keeper's advice.

Water temperature for Brown Trout
Warm — slow
20°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 19.6°C — above the brown trout caution line (18°C). Fish dawn or dusk only. Land it fast, wet hands, no air shots.
Hatch timeline · todayPeak at 6pm

Hatch predictions

Today's headline hatch shown — see all 9 active hatches hour by hour with Pro.

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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 · August highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
1
Grayling seasonSeason
2
1
1
2
2
2
2
2
2
GrannomHatch
2
2
Evening SedgeHatch
2
3
3
3
2
Large Dark OliveHatch
1
2
2
1
Iron BlueHatch
1
2
2
1

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.
  • Walloon permit required, but some stretches may sit under additional society, forest-zone or local rights structures depending on section.
What's coming
Plan ahead
5-day outlook
Water here around 20°C. Nothing cooler within range — carry a thermometer.
Gallery · 2
  1. Semois — File:Frahan JPG01.jpg
    File:Frahan JPG01.jpg
  2. Terrain map of the venue
    Terrain map
Water quality (WFD)
  • Ecology: Moderate
  • Chemical: Failing to achieve good
What this classification means

WFD re-coded 2026-06-18: prior id BERW06_SM01R was a wrong-basin code (no row in EEA WISE). Re-mapped to BERW17_SC28R 'Semois III' near the venue coordinate (49.85,5.08, Bouillon area). Status: EEA WISE 2022 (3rd RBMP). Confidence: medium — VERIFY reach against a map (Semois has 4 reaches I–IV). Source: discodata.eea.europa.eu.

WFD classification · BERW17_SC28R

The full read · show the working · for Brown Trout · confidence 80%
How the 30 is built — score × weight = contribution
Temperature30 × 28%8.4
Flow80 × 22%17.6
Clarity15 × 18%2.7
Feeding Time45 × 13%5.9
Pressure80 × 7%5.6
Insect activity47 × 12%5.6
Limiting factor: Water is very coloured — too coloured for Brown Trout= 46
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.
A drop and clear would lift the flow and clarity scores.
The dawn and dusk windows score higher than the midday lull.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout 3rd Saturday of March → 30 September
  • Grayling 1 June → 28 February
Related guides
Grayling Playbookgrayling tacticsEuro Nymphingsubsurface methods
Booking & contacts