July Fishing on the Jefferson River

July weather, stream flows, and summary

With stream flows dropping drastically throughout the month of July on the Jefferson River, fishing changes as well. Early July sees a Montana river that fishes as well as any other in the state, but by month's end low stream flows often combined with high air temperatures mean warm water, which means less active trout. Simply put: if more water could stay in the Jefferson River in July—it is used heavily by ranchers to irrigate feed for livestock—the river could be one of the best in the West. 

Because the weather in July is the warmest of the year, the low stream flows coupled with high air temperatures make the Jefferson River a good option early in July but a less desirable option by the latter part of the month. Early July sees average daily high air temperatures in the high 70 degrees F while by month’s end the average daily high temperatures rise to almost 85 degrees F. Measurable precipitation is only likely to fall on less than five days throughout the month. July is hot and dry on the Jefferson River and the habits of trout reflect that. 

July fishing: what to expect

Early July on the Jefferson River sees stream flows drop drastically throughout the month. Because of this, anglers on the Jefferson River may shift from floating early in July to walking-and-wading later in the month. With such a drastic drop in stream flows flexibility and managing expectations is paramount on the Jefferson River in July. 

Hatches of Pale Morning Dun (PMDs) mayflies and caddis can be strong in early July. By month’s end, tricos and terrestrials dominate the dry fly charts but water temperatures in the high 60 degrees F often mean most trout cease feeding. Because the Jefferson River is home to Yellow Sally stoneflies, midges, mayfly, and caddis species, these aquatic insects are active subsurface and if water temperatures remain below 65 degrees F anglers can find actively feeding trout. However, by mid-July this is the exception rather than the norm. 

Anglers choosing to fish a two-fly weighted nymph rig will find some success. Choose any combination of the following: stonefly nymphs in sizes 8 through 12, mayfly nymphs in sizes 14 through 20 or caddis pupae in sizes 14 through 18. 

If water temperatures stay in the low 60 degrees F look for hatches of PMDs, caddis, and tricos. A few late hatching stoneflies may occur, but they will be seen early in the morning. Terrestrials may be abundant as well. 

For PMDs choose mayfly dries or emergers in sizes 12 through 16. For PMD nymphs choose beadhead Pheasant Tails in size 12 through 16. For caddis, choose dry flies in sizes 12 through 18 and nymphs in sizes 12 through 18 as well. Most caddis adults will be tan or olive in color. 

Streamer anglers may find aggressive trout in July, particularly in the lowlight conditions of early morning or late evening. Choose white, yellow, black, or black/brown sparsely dressed patterns in sizes 4 through 8. 

Where to find July trout on the Jefferson River

Caddis, small stonefly, and mayfly nymphs are active on the Jefferson River in July. Terrestrials begin to show up in good numbers by the end of the month. Because hatches are strong and terrestrials are abundant, trout on the Jefferson River can be found in a variety of places. 

If fishing nymphs or dry flies, look for trout throughout all possible feeding lies—near bankside structure, seam lines between slow and fast water, shallow flats, riffle corners, and the heads of deep pools. 

For fishing streamers on the Jefferson River in July target the typical predator-prey hangouts. In July on the Jefferson River large brown trout often lie in deeper holes, along undercut banks, or the tailouts of longer runs. Because most days in July consist of bright sunshine, most brown trout on the Jefferson River are found early or late in the day or in deeper water. 

During July on the Jefferson River trout are most often found along the bank, in riffles, shelfs, the heads of runs, and the tail outs of runs. These habitats all offer the primary needs for trout: available food source, cover from predators, cover from strong currents, and flowing water for oxygen. 

Important July hatches

Because the Jefferson River sees a substantial drop in stream flows throughout the month, hatches vary greatly from early to late in the month. Throughout the month caddis and Pale Morning Dun (PMDs) mayflies make up the bulk of July hatches on the Jefferson River, with terrestrials showing up mid-month and lasting throughout the month. 

A variety of caddis species ranging in size from 10 to 20 live in the Jefferson River and hatch throughout the month, occurring at various times throughout the day. PMD hatches typically begin mid-morning and last for several hours. Insects range in sizes from 12 to 18, with most being size 16. As a mayfly, it is important to understand trout may feed on emerging PMDs and not exclusively on fully hatched adults. 

Terrestrials—insects that live the entirety of their life on land—provide a large portion of a Jefferson 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 targets of trout as well. 

Trico mayflies hatch in July on the Jefferson River as well. These small mayflies—sizes 18 through 22—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. 

Jefferson River fly box for July

Caddis pupae size 12 to 16

Caddis CDC emergers size 12 to 16

Caddis dry flies with dark grey, black or brown bodies in size 12 to 16

PMD dry flies size 14 to 18

PMD emergers size 14 to 18

PMD nymphs size 14 to 18

Stonefly nymphs in brown and black in sizes 8 through 12

Sculpin patterns in sizes 2 to 6

Crayfish patterns in sizes 6 to 10

Streamers in white, yellow, black or brown in sizes 2 to 6

Grasshoppers, ants, beetles, and crickets in sizes 6 to 10.

Trico mayfly adults and spinners in sizes 18 through 22