Rules at a glance
- Free fishing
Water temperature for Rainbow Trout
Cool — slow5°C est.ideal 10–18°C
0°14°28°
How to fish it · for Rainbow Trout
When
Season runs 1 June to 14 October — deliberately late, because the Lys carries too much glacial meltwater to fish well before then. Mornings are clearer than afternoons once the glacier gets going for the day.
Where
The three-kilometre reserve above Gressoney-La-Trinité — pocket water and pools typical of a Monte Rosa torrent, restocked weekly.
Method
Bait, spinning or fly all permitted; no catch-and-release requirement. Minimum size 25cm, six fish per permit, up to three permits a day.
Kit
9 ft #5/6, floating line — nothing needs to be delicate here, the water is rarely gin-clear.
Why this works
Fair — water clarity is working for you, but insect activity is the limiting factor today.
Likely species
Mayflies
Mayflies- Anglers curse mayfliesMost likelyLower confidenceNearest relative#20–22 · SpinnerGo tiny: 20-22 spent spinner, single fly, long tippet.
- Ephemera vulgata (lake mayfly)Also possibleLower confidenceNearest relative#8–10–12 · NymphLarge lake/slow-river mayfly; burrows soft sediment.
- Turkey BrownAlso possibleLower confidence#14–16 · DunSmall spring dun on slower glides and margins.
- Late March BrownAlso possibleLower confidence#12–14 · DunLate-season upland riffle dun, dusk emergence.
Caddisflies
Caddisflies- Net-spinning caddis (S. Europe)Most likelyLower confidenceNearest relative#12–14–16 · PupaWidespread riffle net-spinner; evening emergence.
- Green SedgeAlso possibleLower confidenceNearest relative#10–12–14–16 · NymphFree-living green caddis larva; fast stony riffles.
- CapererAlso possibleLower confidence#10–12 · AdultBig autumn sedge; fish dry at last light.
Stoneflies
Stoneflies- Little Brown StoneMost likelyLower confidence#16–18 · AdultSmall dark stone nymph or adult in early spring.
- NeedleflyAlso possibleLower confidenceNearest relative#16–18 · AdultSmall slender stonefly; clean, cold headwater riffles.
Hatch timeline · todayPeak at 10h
Hatch predictions
Today's headline hatch shown — see all 2 active hatches hour by hour as a supporter.
Start free trial14-day free trial. Cancel anytime.
Evidence
Survey-backed · regionalHigh confidence
Backed by regional invertebrate surveys; no sampling on this exact reach yet.
Through the year
0–3 scale · September highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Freshwater ShrimpHatch
2
3
3
3
3
3
3
3
3
3
3
2
Large Dark OliveHatch
1
2
2
1
Blue Winged OliveHatch
1
2
2
2
2
1
Autumn OliveHatch
1
2
1
Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.
Ranked for today
Fly box · Rainbow Trout
8-12 · Pattern
Retrieve, sub-surface
Permits & access
Permit required — see local rules.
- Managed tourist reserve — daily permit required, weekly stocking
- Minimum size 25cm, 6 fish per permit, maximum 3 permits per angler per day
- No catch-and-release requirement.
What's coming
Plan ahead
5-day outlook
Other water nearby · 4
Gallery · 2
Terrain map
The full read · show the working · for Rainbow Trout · confidence 75%
How the 57 is built — score × weight = contribution
Temperature26 × 28%7.3
Flow80 × 22%17.6
Clarity85 × 18%15.3
Feeding Time70 × 13%9.1
Pressure75 × 7%5.3
Insect activity22 × 12%2.6
Conditions total= 57
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitysurvey-backed invertebrate datasurvey
What would change the calculation
Warmer water — toward the 10–18 °C ideal band — would lift the temperature score.
Directions
Seasons & zones
- Rainbow trout 2026-06-01 → 2026-10-14
Related guides
Booking & contacts
Lys
Water temperature for Rainbow Trout
Cool — slow5°C est.ideal 10–18°C
0°14°28°
How to fish it · for Rainbow Trout
When
Season runs 1 June to 14 October — deliberately late, because the Lys carries too much glacial meltwater to fish well before then. Mornings are clearer than afternoons once the glacier gets going for the day.
Where
The three-kilometre reserve above Gressoney-La-Trinité — pocket water and pools typical of a Monte Rosa torrent, restocked weekly.
Method
Bait, spinning or fly all permitted; no catch-and-release requirement. Minimum size 25cm, six fish per permit, up to three permits a day.
Kit
9 ft #5/6, floating line — nothing needs to be delicate here, the water is rarely gin-clear.
Why this works
Fair — water clarity is working for you, but insect activity is the limiting factor today.
Likely species
Mayflies
- Anglers curse mayfliesMost likelyLower confidenceNearest relative#20–22 · SpinnerGo tiny: 20-22 spent spinner, single fly, long tippet.
- Ephemera vulgata (lake mayfly)Also possibleLower confidenceNearest relative#8–10–12 · NymphLarge lake/slow-river mayfly; burrows soft sediment.
- Turkey BrownAlso possibleLower confidence#14–16 · DunSmall spring dun on slower glides and margins.
- Late March BrownAlso possibleLower confidence#12–14 · DunLate-season upland riffle dun, dusk emergence.
Caddisflies
- Net-spinning caddis (S. Europe)Most likelyLower confidenceNearest relative#12–14–16 · PupaWidespread riffle net-spinner; evening emergence.
- Green SedgeAlso possibleLower confidenceNearest relative#10–12–14–16 · NymphFree-living green caddis larva; fast stony riffles.
- CapererAlso possibleLower confidence#10–12 · AdultBig autumn sedge; fish dry at last light.
Stoneflies
- Little Brown StoneMost likelyLower confidence#16–18 · AdultSmall dark stone nymph or adult in early spring.
- NeedleflyAlso possibleLower confidenceNearest relative#16–18 · AdultSmall slender stonefly; clean, cold headwater riffles.
Hatch timeline · todayPeak at 10h
Hatch predictions
Today's headline hatch shown — see all 2 active hatches hour by hour as a supporter.
Start free trial14-day free trial. Cancel anytime.
Evidence
Survey-backed · regionalHigh confidence
Backed by regional invertebrate surveys; no sampling on this exact reach yet.
Through the year
0–3 scale · September highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Freshwater ShrimpHatch
2
3
3
3
3
3
3
3
3
3
3
2
Large Dark OliveHatch
1
2
2
1
Blue Winged OliveHatch
1
2
2
2
2
1
Autumn OliveHatch
1
2
1
Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.
Ranked for today
Fly box · Rainbow Trout
8-12 · Pattern
Retrieve, sub-surface
Permits & access
Permit required — see local rules.
- Managed tourist reserve — daily permit required, weekly stocking
- Minimum size 25cm, 6 fish per permit, maximum 3 permits per angler per day
- No catch-and-release requirement.
What's coming
Plan ahead
5-day outlook
Other water nearby · 4
Gallery · 2
Terrain map
The full read · show the working · for Rainbow Trout · confidence 75%
How the 57 is built — score × weight = contribution
Temperature26 × 28%7.3
Flow80 × 22%17.6
Clarity85 × 18%15.3
Feeding Time70 × 13%9.1
Pressure75 × 7%5.3
Insect activity22 × 12%2.6
Conditions total= 57
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitysurvey-backed invertebrate datasurvey
What would change the calculation
Warmer water — toward the 10–18 °C ideal band — would lift the temperature score.
Directions
Seasons & zones
- Rainbow trout 2026-06-01 → 2026-10-14
Related guides
Booking & contacts