Reservoir · Mixed · Idaho

Island Park Reservoir

Aerial view of Island Park Dam holding back Island Park Reservoir, with the Henrys Fork River flowing out below the spillway

Island Park Reservoir is the impoundment on the Henrys Fork that feeds the famous river below it, a broad, fertile, weed-rich stillwater up in the Island Park caldera holding rainbows and a few big browns.

Fair · Rainbow
Callibaetis Nymph · 12-16
Fairlive now
Evening session looks promising at Island Park Reservoir
Water temperature is the limiting factor today, not the wave. Fish dawn or dusk if you go at all, and handle everything with extra care.
51% confidence
What moved it
  • WindW 4 km/hCalm
Today's fly
CN
Callibaetis Nymph12-16
High-confidence seasonal pick
Conditions on the water
Live gauge
Wind
Calm
W 4 km/h
N
W
from the west
WaveFlat calm
Water temp—
Air temp25°C
CloudClear
Pressure1016 hPa
Rain · recent0.0 mm

Some readings unavailable — check directly before fishing.

How to fish it · for Rainbow
When
Conditions are not ideal but fishable at Island Park Reservoir. Flat calm means fish may be spookier — longer leaders and subtler flies will help. Very warm conditions — trout have a narrower safe zone of cool, oxygen-rich water. Fish only at first light or last light, use barbless hooks, keep fish in the water during release, and stop if fish struggle to recover. Evening can bring a surface rise — have a dry fly or emerger ready.
Where
Start with Callibaetis Nymph (12-16) on a slow figure-of-eight retrieve. Rainbows respond to more active retrieves — try short strips between pauses. If that does not produce, switch depth or speed before changing the pattern entirely.
The plan
Plan A

Start with Callibaetis Nymph (12-16) on a slow figure-of-eight retrieve. Rainbows respond to more active retrieves — try short strips between pauses. If that does not produce, switch depth or speed before changing the pattern entirely.

Plan B

Fish early and late, try deeper during the heat of the day with a fast-sinking line.

Watch for

Evening tends to be the best period in summer — stay late if you can for a sedge or spinner fall.

Either bank or boat

Calm evenings can fish well from bank or boat — target rising fish wherever you find them.

Sub-surface · on the nymphunder the surface

Hatch predictions

See the full sub-surface read with Pro.

Start free trial

14-day free trial. Cancel anytime.

Beyond the hatch · worth watchingambient prey

Hatch predictions

Top prey shown — see all 4 with Pro.

Start free trial

14-day free trial. Cancel anytime.

Through the year
0–3 scale · July highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Gray DrakeHatch
2
2
CallibaetisHatch
2
3
3
3
2
Hexagenia (Western)Hatch
2
2
Black MidgeHatch
2
3
3
3
3
3
3
3
3
3
3
2

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

Ranked for today
Rainbow fly box
Permits & access
Permit required — see local rules.
  • Idaho stillwater regulations — check Idaho Fish & Game
  • Level swings with irrigation draw.
What's coming
Plan ahead
5-day outlook
Condition match
41%
Cloud25%
Wind65%
Temp25%

Conditions are away from Island Park Reservoir's sweet spot — it usually fishes best in ripple wind with cloud skies.

Fishing better nearby · 5
Henrys Fork
11 km
79
Rainbow trout
Warm River
34 km
15
Rainbow trout · Brook trout
Henrys Lake
29 km
Cutthroat trout · Brook trout
Cliff Lake
41 km
Rainbow trout · Brown trout
Wade Lake
47 km
Rainbow trout · Brown trout
Gallery · 2
  1. Aerial view of Island Park Dam holding back Island Park Reservoir, with the Henrys Fork River flowing out below the spillway
    Island Park Dam and Reservoir on the Henrys Fork
  2. Terrain map of the venue
    Terrain map
About this water

Island Park Reservoir is the impoundment on the Henrys Fork that feeds the famous river below it, a broad, fertile, weed-rich stillwater up in the Island Park caldera holding rainbows and a few big browns. It's a boat-and-tube fishery, played with leeches, damsels, and chironomids over the weed beds and along the dam face. The fishing swings with the reservoir level and the irrigation draw, and it can get warm and weedy by late summer. Spring and fall, with the caldera rim all around and the big fish on the move, it's a fine, underrated stillwater.

  • Reservoir
  • Mixed
Water quality · US Clean Water Act
  • Aquatic life: Not assessed
What this classification means

EPA ATTAINS assessment unit 'Island Park Reservoir' (ID17040202SK020L_0L), 2022 Integrated Report. Aquatic Life use: Not Assessed. 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) · ID17040202SK020L_0L

Why this score
  • summer conditions with clear skies and calm wind.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • TroutSaturday of Memorial Day weekend → 30 November
Related guides
Big Stillwater Playbookreservoir tacticsReservoir Entomologymatching the hatchThermal Layers & Troutreading depth and temperature
Booking & contacts