July weather, stream flows, and summary
The Bighorn River in July is a Montana trout river tailor-made for some of the fly fishing’s best attributes. With a variety of hatches, cold and clear water, and opportunities for equally good float-and walk-and-wade fishing, July fly fishing on the Bighorn River is as good as it gets.
With strong hatches of Pale Morning Dun (PMDs) mayflies, caddis, tricos, and a variety of terrestrials, trout on the Bighorn River in July have plenty of available food. This means anglers also have plenty of opportunity to catch some of the Bighorn River’s strong and healthy fish.
Fly fishing on the Bighorn River in Montana consists of nearly 30 miles of flowing water downstream of the afterbay at Yellowtail Dam. Downstream of the dam flows clear and cold water that provides ample habitat for hatches and trout. The majority of the quality trout habitat occurs from the afterbay downstream to Mallards Landing Fishing Access Site. In these thirty miles of river, only three other access sites are available. From the Afterday Access Site to Bighorn Fishing Access Site is thirteen miles of river, this section provides the highest concentration of fish—well above 4,000 trout per mile. For good reason, most anglers only fish the river above Bighorn Access site.
Weather in July is pleasant, if not hot compared to other rivers. Daytime high temperatures average in the mid-80 degrees F throughout the month, with potential for a 90- or 100-degree F daily high temperatures. With an average monthly precipitation of less than 0.5 inches of rain, July is usually sunny and dry. Because the Bighorn River’s stream flows originate from a bottom-release dam, water temperatures in July are almost always trout friendly, staying below 65 degrees F.
Floating is the primary method to fish the Bighorn River, but most anglers use the boat as a form of transportation, getting out of the boat to walk-and-wade fish an area. Stream flows in July historically average around 5,000 cubic feet per second (cfs) early in the month, dropping to below 3,000 towards the end of the month. This gradual drop in flows creates ideal conditions for float and walk-and-wade fishing nearly every day of the month. When flows are below 3,500 cfs many walk-and-wade anglers utilize the access sites and then walk upstream or downstream.
July fishing: what to expect
July on the Bighorn River can feel like a river of two distinct personalities. Because stream flows can vary greatly from early July to late-July, anglers fishing the Bighorn River in July need to be prepared for subsurface nymph fishing as well as sight-casting to rising trout. Stream flows dictate which method will prove the most successful.
If stream flows are above 6,000 cubic feet per second (cfs) expect most fishing to subsurface. For tandem nymph rigs most Bighorn River anglers use 9- to 12-foot leaders with 4X and 5X fluorocarbon tippets. Proven patterns are pink or tan Ray Charles, WD-40s, Little Green Machines, Zebra Midges, and a variety of caddis pupae. Most nymphs should be size 18 to 22.
Even at stream flows above 6,000 cfs caddis and Pale Morning Dun (PMDs) mayflies can hatch. However, the river is flowing fast and full at these flows so the available habitat in which fish can hold and rise to hatching insects is limited.
If flows drop below 3,000 cfs, the dry fly fishing to rising trout on the Bighorn River can be some of the best in the world. Hatches of PMDs, tan and black caddis, and tricos, along with abundant terrestrials paired with water temperatures in the mid-50s, create nearly thirty miles of spring creek-like, match-the-hatch fly fishing. On the Bighorn River dry fly anglers fish nothing shorter than 12-foot leaders and often use 5X and 6X, supple, monofilament tippets.
During July, streamer anglers on the Bighorn River may find some success. Light-colored patterns will work better than dark-colored ones, especially in the bright summer sunshine. During lowlight conditions of early morning or evening, sparsely dressed streamers in black, brown, or olive swung through a riffle could produce some exciting action.
The Bighorn River is home to large populations of scuds and sowbugs. Even during the heart of summer with abundant hatches of caddis and PMDs, Bighorn River trout still feed on scuds and sowbugs. Dead drifting Ray Charles, Firebead Sowbugs, Carpet Bugs, and other scuds and sowbugs on tandem nymph rigs is a proven tactic in July if trout are not rising to caddis, PMDs, or terrestrials.
Where to find July trout on the Bighorn River
July on the Bighorn River typically sees stream flows in the range of 6,000 to 2,000 cubic feet per second (cfs). Compared to other rivers in Montana during July, this is a large volume of water. The Bighorn River occupies a large valley floor and its habitat consists of braids, island channels, and shallow flats.
Pale Morning Duns (PMDs) hatch in July on the Bighorn River. These hatches can be very strong and many of the river’s trout will move to shallow flats, riffles, and runs to feed on emerging nymphs or floating adults. Look for trout in faster currents along riffle corners and seams, medium-speed currents on shallow flats or long runs. As the hatch diminishes later in the day, look for eddys where PMD adults may have stacked-up.
Tan and black colored caddis are very common on the Bighorn River. During a caddis hatch, look for trout in fast, shallow areas of the river. Target water with a stream bottom made of small rocks or pebbles along with surface seams of medium fast water near slow water. With the Bighorn River’s numerous long runs and flats, look for larger fish to feed at the tail-end of these flats and long runs.
Terrestrials—grasshoppers, ants, beetles, crickets, and any other insect that may find itself in the water—make up a sizable portion of a Bighorn River trout’s diet in July. Because the Bighorn River floats north to south and the prevailing winds are westerly, terrestrials are numerous on the Bighorn River. When fishing a terrestrial, focus on all possible feeding lies—near bankside structure, seam lines between slow and fast water, currents flowing along bank-side structure, shallow flats, riffle corners, and the heads of deep pools.
Trico mayflies hatch in July on the Bighorn River as well. During an emergence of tricos, look for trout to hold and feed along bank-side seams or the softer, inside seam of a mid-river riffle or shelf. Tricos hatch at sunrise so after mid-day it is unlikely fish will continue to feed on tricos.
Important July hatches
The dominant hatches on the Bighorn in July River are Pale Morning Duns (PMDs), caddis, and trico mayflies. PMDs and caddis—both black and tan—can be very thick at times. With the Bighorn River’s abundance of long riffles and shallow flats and a stream bead of cobble-sized rocks, the river is home to ideal habitat for PMDs and caddis.
Emerging out of riffles and flats, PMDs create ample opportunities for floating and wading anglers. Caddis hatches can last throughout the month. Most caddis on the Bighorn River are sizes 14 through 18 and most PMDs are sizes 14 through 18 as well. Tan and black caddis are the primary caddis species. In late July many die-hard anglers fish well into dark as hatches of black caddis can be very strong.
Trico mayflies hatch in the early morning hours. Trout rarely feed on trico nymphs but will often rise to adults floating on the surface or “spent” adults—insects that have mated and are now dead.
Terrestrials—insects that live the entirety of their life on land—provide a large portion of a Bighorn River trout’s diet in late July. Grasshoppers, crickets, ants, beetles, spiders, and any other land-dwelling insect that may inadvertently find its way onto the surface will be targeted by trout as well.
Midges are active year-round on the Bighorn River and make-up a massive chunk of a Bighorn River trout’s diet. Fishing midge patterns is best done subsurface as part of a weighted two fly rig.
Scuds, sowbugs, aquatic worms, and crane flies are abundant in the Bighorn River, with sowbugs most likely accounting for over half or a Bighorn River trout’s diet. Strictly subsurface, scuds and sowbugs are not exactly what an angler may think of when it comes to hatches. Often thought of as the same insects, a scud resembles a freshwater shrimp and a sowbug looks like a “rollie-pollie” bug. Especially if hatches of caddis, PMDs, or terrestrials are minimal, a trout on the Bighorn River in July often gobbles-up a well-presented scud or sowbug.
Bighorn River fly box for July
Caddis pupae size 14 to 18
Caddis CDC emergers size 14 to 18
Caddis dry flies with tan or black bodies in size 14 to 18;
PMD dry flies size 14 to 20
PMD emergers size 14 to 20
PMD nymphs size 14 to 20
Trico nymphs in sizes 18 to 22
Trico duns/adults in sizes 18 to 22
Trico spinners in sizes 18 to 22
Grasshoppers, in tan or yellow, in sizes 4 to 14
Ants, crickets, and beetles in sizes 12 to 18
Scuds in sizes 10 through 20
Sowbugs in sizes 10 through 20
Midges, especially Zebra midges in black and olive, in sizes 16 through 22
Sculpin patterns in sizes 2 to 6
Streamers in olive, black or brown in sizes 2 to 6