Fly Fishing Moose Creek, Idaho: A Hidden Eastern Idaho Gem

Two Miles East of Mack’s Inn

Moose Creek enters the Henrys Fork from the south, between Big Springs and Mack’s Inn in the Island Park country of eastern Idaho. Fish and Game maps it at 13.1 miles, all in Fremont County. The mouth sits about two miles east of Mack’s Inn and two miles below Big Springs, near 6,300 feet.

The Big Springs Loop Road leaves U.S. 20 at Mack’s Inn and runs 4.5 miles east to the springs. It crosses Moose Creek less than half a mile above the mouth, at the spot where the USGS has measured the creek since 1924. From there the creek drains the lodgepole plateau to the east, toward the Yellowstone National Park boundary.

The river it joins is unusual. Big Springs pours out more than 120 million gallons a day at a constant 52 degrees, which makes the upper Henrys Fork a spring creek from its first mile. Moose Creek is the snowmelt stream on the side of it.

For more small waters in this state, see our Idaho secret waters guide.

Regulations (Checked September 2026)

Moose Creek is not named in Idaho’s 2025 to 2027 rule book. Fish and Game’s Fishing Planner page assigns it the “Henrys Fork tributaries” special rule, the same rule that covers Sheridan Creek. Upper Snake Region general rules fill in the rest.

The rule that matters most here is not on the creek. The Henrys Fork itself, from the Henrys Lake Outlet upstream to the head of Big Springs, is closed to fishing, and Moose Creek enters inside that closed section. You can fish the creek, but not the river at its mouth.

Below the Outlet the river opens up. From McCrea Bridge upstream to the Henrys Lake Outlet, the Henrys Fork runs on a winter catch-and-release rule, except brook trout, and a summer trout limit of six. That is the water past Mack’s Inn and Flatrock Campground.

The Upper Snake Region office in Idaho Falls answers at (208) 525-7290.

The Fish: Brook and Rainbow, Managed as Wild

Fish and Game’s 2022 survey of Moose Creek recorded two species, brook trout and rainbow trout. The department’s 2025 to 2030 fisheries plan lists “Moose Creek and tributaries,” 20 miles, as wild rainbow and brook trout water with one direction: manage for wild trout.

That is narrower than the old advice about this creek. Nobody planted brook trout here as far as the stocking database knows. The trout plants on record are rainbows, a dozen small batches of 350 to 5,000 fish between 1968 and 1984, and 2,000 catchable Yellowstone cutthroat in May 1986. No cutthroat has turned up in a survey since.

The big numbers in the stocking record are not trout at all. From 1968 to June 2000, Fish and Game put about 3.6 million kokanee fry and fingerlings into Moose Creek, 579,000 of them in one week of June 2000. Nothing has been stocked since.

The Kokanee That Used to Run Here

Moose Creek was once one of the great kokanee spawning streams in eastern Idaho. Fish and Game’s regional biologist told the Associated Press in 2013 that 50,000 to 60,000 adult kokanee ran up the creek from Island Park Reservoir every fall. There were so many that the department took eggs here each year to supply its statewide kokanee program.

A longtime Island Park summer resident put it more plainly. The creek was “blood red with kokanee,” and you heard you could walk across on their backs.

Then the state moved its egg-taking elsewhere, and the run fell apart. Three years of surveys found no spawners.

In September 2013 a crew electrofished the Henrys Lake Outlet, spawned 59 pairs of kokanee, and placed about 75,000 eggs in streamside boxes in Lucky Dog Creek and in Moose Creek. The idea was that fry would imprint on the creek and come back as adults.

Fish and Game’s 2025 to 2030 plan reports the result. The stockings in Moose and Lucky Dog creeks “did not result in a return of adult spawning fish in subsequent years,” despite eyed eggs in incubators and artificial redds.

A remnant wild run survives in the Henrys Lake Outlet below the North Big Springs Loop bridge, in the hundreds rather than thousands, and those wild fish make up most of the reservoir’s kokanee.

The plan blames the reservoir more than the creeks. In summer the cold water at depth has no oxygen, and the oxygenated water on top is too warm for salmon, so usable habitat shrinks from mid-June through September.

A local outdoors columnist offered a second reason in 2021: the traditional spawning streams like Moose Creek “were ruined during the Yellowstone fires” of 1988.

Flows

No gauge has ever run continuously on Moose Creek. What the USGS has is 26 spot measurements at the Big Springs Loop Road crossing, taken between 1924 and 2015.

Source: USGS site 13040800, field measurements.

Two things stand out. The creek peaks with the snowmelt in May, so it is not the pure spring creek the old guides described. And late-summer flow swings with the snowpack, from the high 80s in wet years to the mid-teens in the drought years of 2001 to 2003 and 2015.

For timing, the nearest live snowmelt gauge in the basin is the Fall River near Squirrel, which averages 1,598 cubic feet per second in May, 1,463 in June, and 441 in July. It drains a different plateau, so use it only for the shape of the year. Runoff settles by mid-July, and the creek fishes from then into October.

Getting There

This is grizzly country. The Caribou-Targhee’s food storage order requires food and garbage to be secured in an approved way, with no camping within 100 yards of unsecured food or a quarter mile of an unsecured carcass.

The bears shape bigger decisions too. When the Bureau of Reclamation studied new dams for the Henrys Fork basin, it dropped a 60,000 acre-foot dam site on Moose Creek because the ground behind it was occupied grizzly habitat.

How to Fish It

Moose Creek is small water, 15 to 90 cubic feet per second by late summer, in Island Park’s lodgepole and meadow country. A 3- or 4-weight rod, an attractor dry in sizes 12 to 16, and a small dropper nymph will cover it. Fish it upstream and keep a low profile. Our dry fly tips cover the presentation side.

Know the calendar. From Memorial Day weekend to the end of November you may keep six trout, and brook trout are keepable in any season with a limit of 25. In winter and spring every rainbow goes back.

Kokanee carry a regional limit of 15, but the whole point of two decades of work here is to get spawners back, so leave any red fish alone in the fall.

Do not fish the Henrys Fork at the mouth. It is closed from the Henrys Lake Outlet up to the head of Big Springs. If you want the main river, fish it below the Outlet at Mack’s Inn, where the six-trout summer rule applies.

Two other eastern Idaho waters go with this one. Sheridan Creek runs under the same Henrys Fork tributaries rule into the west arm of Island Park Reservoir, and Bear Creek feeds Palisades Reservoir to the south.

Frequently Asked Questions

Where is Moose Creek in Idaho?

Moose Creek is a 13-mile tributary of the Henrys Fork in Fremont County, in the Island Park area of eastern Idaho. It enters the river from the south about two miles east of Mack’s Inn and two miles below Big Springs, near 6,300 feet. The Big Springs Loop Road crosses it less than half a mile above the mouth.

What are the fishing rules on Moose Creek?

Fish and Game’s planner assigns it the Henrys Fork tributaries rule. From December 1 to the Friday before Memorial Day weekend, trout are catch-and-release except brook trout. Then through November 30 the trout limit is six, no cutthroat kept. Brook trout limit 25. No bait ban, no barbless rule. The Henrys Fork at the mouth is closed to fishing.

When is the best time to fish Moose Creek?

Mid-July through October. There is no gauge, but USGS spot measurements show a runoff peak of 116 cubic feet per second in mid-May 1996 and late-summer flows of 15 to 87 depending on the year. The Fall River gauge in the same basin peaks in May and June and settles by mid-July. Late summer and fall are the reliable window.

What fish live in Moose Creek?

Fish and Game’s 2022 survey found brook trout and rainbow trout, and its management plan handles the creek as wild trout water. Kokanee once ran here by the tens of thousands from Island Park Reservoir, but the run collapsed and a 2013 restoration attempt did not bring adults back. The creek was last stocked in June 2000, with kokanee fingerlings.

Sources and Check Dates

• Idaho Department of Fish and Game, Fishing Seasons and Rules 2025–2027, second edition 2026: Upper Snake Region pages 41–43, including the Henrys Fork sections and the Henrys Fork tributaries rule. Checked September 2026.
• IDFG Fishing Planner, Moose Creek: species surveys, stocking records, and rules block; IDFG hydrography layer for the creek’s course and mouth. Checked September 2026.
• IDFG, Fisheries Management Plan 2025–2030: Henrys Fork drainage tables and the Island Park Reservoir narrative. Checked September 2026.
• Associated Press via the Idaho State Journal, “Biologists eye return of kokanee to East Idaho creek,” September 2013. Checked September 2026.
• Bill Schiess, “‘Sneakers’ complicate spawning kokanee,” East Idaho News, September 4, 2021, used for the fire remark only.
• USGS site 13040800, Moose Creek near Big Springs: field measurements 1924–2015. USGS gauge 13047500, Fall River near Squirrel: monthly means 1993–2025. Checked September 2026.
• USDA Forest Service, Caribou-Targhee National Forest: Big Springs Campground, Flatrock Campground, food storage order, and Ashton/Island Park Ranger District pages. Checked September 2026.
• Jackson Hole News & Guide, “Henrys Fork plan considers 4 new dams,” on the Bureau of Reclamation’s Henrys Fork Basin Study; Henry’s Fork Foundation newsletter, fall 2012. Checked September 2026.
• Wikipedia, Henrys Fork and Big Springs, for the spring’s discharge, temperature, and National Natural Landmark status; OpenStreetMap for road positions relative to the creek.