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Home › Waters › Idaho › Big Lost River
River · Custer County in the Lost River valley of central Idaho, running from the Copper Basin and Wildhorse headwaters past Chilly and Mackay toward the Snake River plain · Idaho

Big Lost River Fishing Guides

A high desert wild trout river under Idaho's tallest peaks, gauged at Howell Ranch on the free-flowing upper reach above Mackay Reservoir.

A freestone river running through a rocky mountain valley in autumn in the Northern Rockies

Map of the Big Lost River

25 numbered points: 7 access points, 5 campsites, 7 bridges, 3 parks and conservation areas, 2 hazards, 1 USGS gauge. Tap a marker for details. Reviewed Sep 16, 2026.

Printable version →
  • Access / boat ramp (7)
  • Campsite (5)
  • Bridge crossing (7)
  • Park / conservation area (3)
  • Dam / hazard (2)
  • USGS gauge (1)
Map data © OpenStreetMap contributors. Points are curated from OpenStreetMap and state agency sources; confirm access and hours before you go.

Print it. Bag it. Bring it.Phones die, screens crack, and most of this water has no signal. Print this map, fold it into a zip-top bag or dry bag with your license, and you have a backup your electronics can’t give you. Every marker is numbered so you can say exactly where you are.

Open the printable map
All 25 points on this map
#PointTypeLat, LonNotes
1Bartlett Point Road Bridge
County road crossing at Howell Ranch		Bridge crossing43.99710, -114.02214
2USGS gauge — Big Lost River at Howell Ranch near Chilly
Station 13120500		USGS gauge43.99833, -114.02111
3Big Lost River — Upper
IDFG access site · state endowment land		Access / boat ramp44.01782, -113.98930
4Old Chilly Road Bridge
County road crossing		Bridge crossing44.05939, -113.87791
5Mackay Reservoir — Upper
IDFG access site		Access / boat ramp43.96791, -113.71068Shoreline access at the head of Mackay Reservoir.
6Mackay Reservoir — Lower
IDFG access site		Access / boat ramp43.96346, -113.70271
7Joseph T. Fallini Campground
BLM Challis Field Office		Campsite43.96137, -113.67952BLM campground on Mackay Reservoir; the agency also lists it as the Mackay Reservoir Recreation Site.
8Mackay Dam
Irrigation dam		Dam / hazard43.95178, -113.67261
9Big Lost River — Lower
IDFG access site		Access / boat ramp43.94085, -113.65016The tailwater access below Mackay Dam.
10City of Mackay Tourist Park
City of Mackay		Park / conservation area43.91177, -113.62207
11River Park RV Park
Private · Mackay		Campsite43.90995, -113.61988
12Marinac Fishing Access
IDFG access site · Smelter Avenue, Mackay		Access / boat ramp43.90269, -113.61692In-town access at the Smelter Avenue crossing.
13White Knob Motel & RV Park
Private · below Mackay		Campsite43.89392, -113.57737
144080 West Bridge
County road crossing		Bridge crossing43.87045, -113.51248
15Stennett
IDFG access site		Access / boat ramp43.85937, -113.47132
16Moose Crossing RV Park
Private		Campsite43.86177, -113.45273
17Rothwell
IDFG access site		Access / boat ramp43.84707, -113.44237The lowest agency access on the Big Lost; below here the river runs through private farmland.
18Moore Diversion
Irrigation diversion dam		Dam / hazard43.78602, -113.35904
193175 North Bridge
County road crossing above Moore		Bridge crossing43.73624, -113.35855
20Moore City Park
City of Moore		Park / conservation area43.73384, -113.36681OSM spells the name with a double space; corrected here.
21Aikele Road Bridge
County road crossing above Arco		Bridge crossing43.63823, -113.32654
22Bottolfsen Park
City of Arco		Park / conservation area43.63227, -113.30431
23Mountain View RV Park
Private · Arco		Campsite43.62637, -113.30538
242400 North Bridge
County road crossing at Arco		Bridge crossing43.62395, -113.31211
25Idaho Medal of Honor Highway Bridge
US 20/26 at Arco		Bridge crossing43.61545, -113.31005The last crossing on this sheet.

Guides on the Big Lost River

Claimed profiles take booking requests. Unclaimed profiles are built from public records so the river is never empty; the guide can claim or remove one any time.

About the Big Lost River

The Big Lost River runs down a wide sagebrush valley between the Pioneer Mountains and the Lost River Range, under Borah Peak and the highest ground in Idaho. It gets its name honestly: below Arco the river sinks into the lava of the Snake River plain and disappears underground, feeding the aquifer rather than ever reaching a sea. The reach that matters to anglers is the upper river, above Mackay Reservoir, where the Wildhorse and Copper Basin headwaters come together and run through a mix of private ranch and public ground.

This gauge sits at Howell Ranch near Chilly, on that free-flowing upper reach. It is a genuinely wild trout fishery with no stocking in the upper river, and the rainbows there are well conditioned, selective and larger than the modest size of the water suggests. Brook trout occupy the headwaters and the tributaries, brown trout appear lower down, and mountain whitefish are abundant and useful in winter. The classic reach below Mackay Dam is a separate tailwater fishery with its own character and its own gauge, and it should not be confused with the water this station reads.

The catch is irrigation. The Big Lost valley is heavily diverted for agriculture, and flows in the middle and lower river can drop dramatically through July and August as headgates open. That makes the discharge number here more operationally important than on most trout rivers – it is the difference between a good wading day and a river reduced to a trickle between pools. Much of the upper valley is private ranch land, so anglers should identify legal access carefully and stay on the public reaches. The gauge reports discharge and stage with no temperature series attached.

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Version 1.0, dated 6 September 2026. Applies to every photograph submitted to GuidedFloats through the contact form, a species page, or the community board.

1. What you give us

By ticking the box on the form you grant Guided Floats, LLC (“GuidedFloats”, “we”) a non-exclusive, worldwide, royalty-free license to store, copy, resize, crop and display your photograph on guidedfloats.com, in GuidedFloats’ own social media accounts and mobile apps, and in material that promotes the site itself, in connection with the fish, water or community feature you sent it in for. The license lasts until you withdraw it (section 4).

You keep the copyright. The license is not exclusive, so you can use the photo anywhere else and license it to anyone else. We will not sell your photo, license it on to anyone else on its own, or use it in paid advertising for a third party.

2. What you confirm

You confirm that you took the photograph yourself (or otherwise own the rights to it), that you have the right to grant this license, and that publishing the photo does not infringe anyone else’s copyright, privacy or other rights.

If any person is recognisable in the photo, you confirm that they have agreed to its being published here, and that a parent or guardian has agreed on behalf of anyone under 18. Please do not send photographs of other people’s catches, screenshots, or pictures copied from other websites or social media.

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We print the credit name you give us beside the photo wherever it appears on the site, and record it as the photo’s creator in the page’s structured data. If you leave the credit blank we use the name you gave us on the form. Write “Anonymous” if you prefer no name at all. Your email address, phone number and the exact spot the photo was taken are never published.

4. Withdrawing the license

You can withdraw the license at any time by emailing hello@guidedfloats.com, or by using the contact form, and telling us which photo you mean. We will remove the photo from guidedfloats.com within 7 days of receiving your message and stop using it in anything new. Copies that are already outside our control — search-engine caches, social posts that have already gone out, printed material already produced — may take longer to disappear or may not be recallable, and we are not responsible for those.

5. What we may do

We choose which photos to publish and may decline any submission without giving a reason. We may crop, resize, sharpen or colour-correct a photo for display, and we may remove a photo at any time. We will not alter a photo in a way that misrepresents the fish, the water or you.

6. Your details

We keep your name, email address, the credit name, the water and date you gave us, and the network address the submission came from, with the submission record, as our evidence of this license. We hold that record for as long as the photo is published and for the retention period described in our privacy policy. Location data that your camera or phone embedded in the file is removed before the photo is published.

7. Versions

The version of this license you accepted is stored with your submission and printed with the photo. A later version does not apply to a photo you have already sent unless you agree to it.

Fished this water? Add a photo

Reviewed by hand before it appears. Pick the water, not the spot — we never publish exact locations.

Never published. We use it only if we need to ask about the photo.

Posting to Big Lost River.

JPG, PNG or WebP, up to 12 MB. We resize it and strip the location data out of the file.

The name shown under the photo. Leave blank to stay anonymous.

Reader photo license v1.0 — the short version:

  • You grant Guided Floats, LLC a non-exclusive, royalty-free license to publish, resize and crop your photo on guidedfloats.com and in GuidedFloats’ own social posts and apps. You keep the copyright and can use the photo anywhere else.
  • You confirm that you took the photo yourself, that publishing it does not infringe anyone else’s rights, and that anyone recognisable in it (or a parent or guardian, if they are under 18) is happy for it to appear here.
  • Credit is printed beside the photo wherever it appears on the site, using the credit name you give us. Leave it blank and we use your name; write “Anonymous” for no name. Your email address is never published.
  • Withdrawing is one email to hello@guidedfloats.com naming the photo. It comes off the site within 7 days.
Read the full license

Version 1.0, dated 6 September 2026. Applies to every photograph submitted to GuidedFloats through the contact form, a species page, or the community board.

1. What you give us

By ticking the box on the form you grant Guided Floats, LLC (“GuidedFloats”, “we”) a non-exclusive, worldwide, royalty-free license to store, copy, resize, crop and display your photograph on guidedfloats.com, in GuidedFloats’ own social media accounts and mobile apps, and in material that promotes the site itself, in connection with the fish, water or community feature you sent it in for. The license lasts until you withdraw it (section 4).

You keep the copyright. The license is not exclusive, so you can use the photo anywhere else and license it to anyone else. We will not sell your photo, license it on to anyone else on its own, or use it in paid advertising for a third party.

2. What you confirm

You confirm that you took the photograph yourself (or otherwise own the rights to it), that you have the right to grant this license, and that publishing the photo does not infringe anyone else’s copyright, privacy or other rights.

If any person is recognisable in the photo, you confirm that they have agreed to its being published here, and that a parent or guardian has agreed on behalf of anyone under 18. Please do not send photographs of other people’s catches, screenshots, or pictures copied from other websites or social media.

3. Credit

We print the credit name you give us beside the photo wherever it appears on the site, and record it as the photo’s creator in the page’s structured data. If you leave the credit blank we use the name you gave us on the form. Write “Anonymous” if you prefer no name at all. Your email address, phone number and the exact spot the photo was taken are never published.

4. Withdrawing the license

You can withdraw the license at any time by emailing hello@guidedfloats.com, or by using the contact form, and telling us which photo you mean. We will remove the photo from guidedfloats.com within 7 days of receiving your message and stop using it in anything new. Copies that are already outside our control — search-engine caches, social posts that have already gone out, printed material already produced — may take longer to disappear or may not be recallable, and we are not responsible for those.

5. What we may do

We choose which photos to publish and may decline any submission without giving a reason. We may crop, resize, sharpen or colour-correct a photo for display, and we may remove a photo at any time. We will not alter a photo in a way that misrepresents the fish, the water or you.

6. Your details

We keep your name, email address, the credit name, the water and date you gave us, and the network address the submission came from, with the submission record, as our evidence of this license. We hold that record for as long as the photo is published and for the retention period described in our privacy policy. Location data that your camera or phone embedded in the file is removed before the photo is published.

7. Versions

The version of this license you accepted is stored with your submission and printed with the photo. A later version does not apply to a photo you have already sent unless you agree to it.

Access

Howell Ranch reach near Chilly - the public water at the gauge itself, reached from the Trail Creek Road.
Wildhorse Creek Road - Forest Service access to the upper headwater forks.
Copper Basin Road - public access to the other main headwater arm above the confluence.
Mackay Reservoir inlet - access where the upper river enters the reservoir.
Highway 93 bridges between Chilly and Mackay - limited roadside access, much of it bordered by private ranch.
Mackay city park and the reach below town - lower-valley bank access.
Bureau of Land Management ground in the Lost River valley - scattered public reaches worth mapping in advance.

Seasons

Spring: snowmelt from the Pioneers and the Lost River Range keeps the river high and off-colour into June.
Summer: the main season, with terrestrial fishing at its best and irrigation withdrawals cutting flows through August.
Fall: flows recover as the headgates close, and the fishing is at its best in cool weather with almost no pressure.
Winter: cold, low and largely inaccessible, with deep snow closing much of the valley road network.

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Questions

What is the current flow on the Big Lost River?

As of Sep 17, 5:00 am, the USGS gauge BIG LOST RIVER AT HOWELL RANCH NR CHILLY ID reads 93 cfs. Conditions update every 15 minutes.

What species can you catch on the Big Lost River?

Anglers target Brook Trout, Brown Trout, Mountain Whitefish, Rainbow Trout on the Big Lost River in Idaho.

Are there fishing guides on the Big Lost River?

GuidedFloats lists 4 guides and outfitters on the Big Lost River. Claimed profiles accept booking requests; unclaimed profiles are built from public records and link to the business.

Where can you access the Big Lost River?

Howell Ranch reach near Chilly - the public water at the gauge itself, reached from the Trail Creek Road. Wildhorse Creek Road - Forest Service access to the upper headwater forks. Copper Basin Road - public access to the other main headwater arm above the confluence. Mackay Reservoir inlet - access where the upper river enters the reservoir. Highway 93 bridges between Chilly and Mackay - limited roadside access, much of it bordered by private ranch. Mackay city park and the reach below town - lower-valley bank access. Bureau of Land Management ground in the Lost River valley - scattered publi...

When is the best time to fish the Big Lost River?

Spring: snowmelt from the Pioneers and the Lost River Range keeps the river high and off-colour into June. Summer: the main season, with terrestrial fishing at its best and irrigation withdrawals cutting flows through August. Fall: flows recover as the headgates close, and the fishing is at its best in cool weather with almost no pressure. Winter: cold, low and largely inaccessible, with deep snow closing much of the valley road network.

Where are the fishing regulations for the Big Lost River?

Regulations change by season and section. Read the current rules on the Idaho agency site: https://idfg.idaho.gov/rules/fish