Mountain Freestone · Granite · Honshū, JP

Itoshiro River

Mount Choshi and Itoshiro River
Tomorrow · Not the day for it
CDC Emerger
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
CDC Emerger
CDC Emerger
Conditions on the water · Tomorrow
Estimate
Level
Moderate rain recently
No gauge reading
Water temp15.3°C
ClarityUnfishable
Weather18°C
WindN 4 km/h
Pressure1017 hPa
Rain · recent24.5 mm
Rain · ahead0.7 mm

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

Water temperature for Rainbow Trout
Ideal
15°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
Good — water temperature is working for you, but insect activity is the limiting factor today.
Likely species
Caddisflies
Damselflies & dragonflies
Hatch timeline · tomorrowPeak at 14:00

12:00(now) — Glossosoma (Japan)

Stage: Taking dunsApproach: Dry flyActivity: 61%
Also:Heather Fly52%Daddy Long Legs45%Isonychia japonica37%
Peak emergence windowWeather boost11 food groups active

Peak activity at 14:00 — Isonychia japonica (Isonychia japonica, 12 food groups active)

Sub-surface · on the nymphunder the surface

Hatch predictions

Top nymph shown — see all 3 guilds as a supporter.

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Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

Supporters see what else is on the menu.

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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
Ephemera japonica (Upstream Keiryu Mayfly)Hatch
2
3
2
Stenopsyche CaddisHatch
2
3
3
2
Cicada (Semi)Hatch
2
2
Epeorus latifolium (Riffle Mayfly)Hatch
2
3
3
3
3
3
2

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

Ranked for today
Fly box · Rainbow Trout
Permits & access
Permit required — see local rules.
  • Local fishery co-operative yugyoken required; spawning closure around 30 September
  • Confirm exact reach and method rules.
What's coming
Plan ahead
5-day outlook
Gallery · 2
  1. Mount Choshi and Itoshiro River
    Alpine river with mountain backdrop.
  2. Terrain map of the venue
    Terrain map
Conservation note

White-spotted char (iwana) and amago — the Pacific-side red-spotted masu trout — with some stocked rainbow.

The full read · show the working · for Rainbow Trout · confidence 65%
How the 61 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow41 × 22%9.0
Clarity45 × 18%8.1
Feeding Time55 × 13%7.2
Pressure75 × 7%5.3
Insect activity32 × 12%3.8
Conditions total= 61
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
  • Char late February to April → late September to mid-October

    Honshu/Shikoku/Kyushu keiryu are managed by local fishery co-operatives — a yugyoken (day/annual ticket) is required, and most streams close around 30 September / mid-October for spawning. Species are surfaced in prose only (no engine slugs for yamame, amago or iwana). Legal status: guidance_not_permission.

Related guides
Euro Nymphingsubsurface methods
Booking & contacts