DIY Guide to Fly Fishing Boulder River in Montana

For the fly fishing angler looking for an adventure, with an element of danger thrown in, the Boulder River in Montana offers just this.

You will not find an abundance of guides and outfitters here, as the conditions are not conducive for drift boats.

The reason we refer to this river as dangerous is the nature of the land where it flows. You will find whitewater conditions and slippery rocks as you wade.

Unfortunately, there have been many tragic accidents as inexperienced rowers have attempted to navigate it. Fortunately, the river has various personalities and wade fishing opportunities are aplenty.

Best Places to Fish the Boulder River

Located in south-central Montana, with a shorter overall length than many of its companion Montana rivers, anglers will find eager to please trout in each section. Above the Natural Bridge State Monument, rainbows, and cutthroats are the predominant fish, ranging upwards of 15 inches.

If you are looking for rainbows and browns, then your attention should be focused on the section below the Natural Bridge State Monument, where they can grow to upwards of 24 inches. However, access will be your challenge to reach these trout as the river flows through private land.

Boulder River Map and Fishing Access Sites

map of fishing access spots on Boulder River in Montana

Get directions to fishing access points and real-time stream flow data with the DIY Fly Fishing Map

If you are willing to wade fish on tricky waters, and walk a ways from your access point, then the Boulder River should be considered. What you can expect is a moderate amount of fishing pressure, certainly not heavy as compared to some of the more popular Montana fly fishing destinations. Slippery, dangerous rocks will need to be navigated as you wade fish. Wading staffs are a necessity in most cases.

Access on the upper section, from its origin and the following 30 miles, is easy. All you have to do is pull your vehicle off to the side of the road and go. On the lower section, below the Natural Bridge State Monument, access is difficult.

The key to accessing the lower portion is to find one of the few access points and wading up or downstream a ways to discover great fishing water. If you stay below the high water marking, you should not give any of the local landowners a grievance. Based on previous anglers experience, they are less likely to complain.

Best Time to Fish the Boulder River

When posed with the question of when the best time of year is to fish the Boulder, the consensus is mid-July through August. The spring months require waiting on the ice to release, and then later on through the early summer there is runoff that creates a torrid, swirling river. With the swells and the fast moving current during this time, wade anglers are best served to wait for better conditions.

Boulder River Flow and Current Conditions

Boulder River at Big Timber MT

  • Streamflow: 120 ft³/s
  • Gage height: 1.74 ft
Streamflow GraphGage height Graph

Boulder River Fishing Tips

With the calmer period from mid-July through August, expect various hatches to occur. These hatches include PMD's, caddis, golden stones, and terrestrials. One of the benefits of fly fishing this river is the trout are not picky. Use nymph patterns to match the above hatches. Additionally, don’t shy away from attractors and terrestrial patterns.

Need flies? 

Ventures Fly Co. offers a great selection of dry flies, nymphs and streamers that will catch fish just about anywhere.  Set includes 40 high quality, hand-tied flies (see list below) and waterproof fly box. 

Dry Flies
- Adams Dry Fly
- Elk Hair Caddis
- Blue Wing Olive
- Royal Wulff
- Griffith's Gnat White
- Stimulator, Organge
- Chernobyl Ant

Nymphs/Wet Flies
- Rubber Leg Nymph, Brown
- BH Pheasant Tail Nymph
- BH Prince Nymph
- BH Hare's Ear Nymph
- Barr's Emerger Nymph
- Zebra Midge Nymph, Black

- Wooly Bugger, Black (Size #8x2)
- Wooly Bugger, Olive (Size #8x2)

Gear Recommendations

A 10-foot 4-wt fly rod with floating line is perfect for fishing dry flies and small nymphs on the Boulder River. For larger nymphs and streamers a 9-foot 5-wt with a sink tip fly line makes life easier. A tapered 9-foot leader, with tippet size 3X to 6X to match the flies you are throwing, is pretty standard.

Need Gear? 

Below are recommendations for essential gear to make the most of your time on the water.

Quality rod, reel, line and rod tube at a reasonable price. Backed by Orvis 25-yr guarantee, a brand you can trust.

High performance nylon leader, great for fishing Dry Flies, Nymphs and Streamers.

Excellent knot strength, stretch and suppleness make this the finest nylon tippet.  3-pack of the sizes you'll need the most.

Heavy duty, waterproof, yet breathable.  If you are tough on waders, these are for you. Backed by Simms Wader Warranty. If they leak, they got your back.

Most durable, yet comfortable, boot on the market.  Excellent foot and ankle support.  Great for rocky rivers. Lightweight and designed for all-day wear.

Sweet pack with ample storage. Unique harness system reduces neck strain. Sleek tapered face improves visibility - you can see your feet when wading!

Durable and lightweight. The carbon fiber frame floats.  Hooks don't get stuck in the rubber mesh bag . Extra length makes it easier to net fish.  Simply the best nets on the market.

Tough, waterproof and priced right. Hold 900+ flies in slotted foam.  If you need more storage - you have too many flies!

Simple, sharp nippers at great price. Clip on retractor keeps this must have gear at your fingertips.

Strong with a fine tip. Perfect for removing split shot and hooks. Simply the best fishing pliers.

The 580 Glass polarized lenses are super clear and somehow relaxing on the eyes.  Game changer.

Note: DIY Fly Fishing earns a commission (at no cost to you) on sales made using the links above. Thank you for your support!

Boulder River Fishing Reports

There are a number of area fly shops that publish Boulder River fishing reports. A few to check out are listed below.

Boulder River Trip Planning Tips

Location of the Boulder River is close to I-90, as it meets the Yellowstone River at the town of Big Timber. For the angler flying in, consider yourself fortunate as the Billings Logan International Airport is a little less than an hour and a half away from Big Timber.

For your lodging needs, options are available in Big Timber, as they have a handful of hotels and Bed and Breakfasts. If you will be camping, consider the Natural Bridge State Park. You will find lodges as well as campsites at this centrally located park near the Boulder River. There is also the Falls Creek, Big Beaver, and Aspen campgrounds, as each of these 3 are located within a short distance of the Natural Bridge State Monument. 

While you are here, be certain to set aside time to experience the Natural Bridge Falls. As the Boulder River makes its way over a limestone rock layer and flows down approximately 100 feet, it creates an aurora that your senses should not miss. Depending on what time of year you visit, you will either see the river flow from the top or you will witness it bursting through the cliff’s wall.

Looking for more places to fish in Montana? Check out our DIY Guide to the Best Fly Fishing in Montana.

Feature Image: Nathan Clement

About the author

Ken is an avid fisherman of 40+ years who loves to explore and find new places to fish. He created DIY Fly Fishing to help you do the same.

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