Montana Fly Fishing 3 min read

DIY Guide to Fly Fishing Boulder River in Montana

Ken Sperry

Posted by Ken Sperry

June 20, 2024

Boulder River 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.

River Overview

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 the Fishing Access Points shown above 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: 234 ft³/s
  • Gage height: 2.27 ft
Streamflow GraphGage height Graph

Best Flies for the Boulder River

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.

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.

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