August weather, streamflow's, and summary
August fly fishing on the Smith River is unique. Unique because an August trip rarely occurs due to the river’s low flows and the potential for high water temperatures. This doesn’t mean that a trip never occurs, but because the Smith River’s stream flows are entirely dependent on the remaining available snowpack, flows in August are often too low to float. Plus, these low flows also mean water temperatures rise to levels too high for consistent hatches and actively feeding trout.
August weather on the Smith River is hot and dry. The first few weeks of August have average daily high temperatures in the mid-80 degrees F. By month’s end the average daily high temperature drops to 78 degrees F. This drop in temperature is helpful for feeding fish but stream flows remain too low to float. Less than 1” of rain falls throughout the month of August.
Because nearly all fishing trips on the Smith River require multiple overnight stays—the main access points are 60 miles apart and anglers must apply for a permit to float and camp on the river. With low stream flows often present in August, there simply is not enough water in the river to float most boats. If a trip were to occur in August, careful planning and a thorough understanding of river conditions and boat-packing would be essential. This includes the following: having the necessary gear, knowing how to prep and prepare meals, some rowing experience, and a knowledge of individual group dynamics. These things are crucial to getting the most out of a Smith River fly fishing trip.
Most anglers spend no less than three and not more than five nights on the river. However, with the low flows of August, making the 60-mile journey in less than four nights would be quite an accomplishment.
The Smith River is the only river in Montana that requires a permit for all outfitted guests and private users to take a multi-day floating and camping trip. There are only a few outfitters that are permitted to operate on the Smith River. Private users can apply for launch via a lottery system operated by Montana Fish, Wildlife and Parks. For launches in August, anglers must apply in February. Information can be found online at Montana’s Smith River State Park.
August fishing: what to expect
For a fly fishing trip on the Smith River in August, expect a river that is a shadow of its usually glamorous self. This isn’t because the fish leave or water quality is poor. It is simply a function of a few factors. First, streamflows are very low which means floating and fishing—the primary way most anglers fish the Smith River—becomes logistically difficult. With average streamflows in August well below 150 cubic feet per second (cfs) floating a boat down the Smith River entails a lot of dragging over rocks and shallow flats. Warm daily air temperatures compounded with low flows create water temperatures above the ideal range for trout. Lastly, hatches are minimal because of low flows and warm water temperatures.
If an option does exist to fly fish the Smith River in August—if access is gained through private land-owner permission or possibly utilizing a shallow water canoe—fishing action will be focused early and late in the day. With low flows and bright sunshine that is common in August, trout on the Smith River may feed on the surface early in the morning and late in the evening. As the water temperature climbs above 68 degrees F, expect trout to retreat to cool, deep water and cease feeding until cooler water temperatures prevail. Because of these high water temperatures, anglers on the Smith River in August should focus entirely on the canyon section—below the Rock Creek confluence and above the Deer Creek confluence.
Pale Morning Duns, caddis, and stonefly nymphs are active year-round, but during August these nymphs are much more active when water temperatures are below 65 degrees, so it is a good idea to get an early start. Trico mayflies—tiny black-bodied mayflies—can hatch on the Smith River around sunrise. These mayflies are small, with most being size 18 to 22. For dry fly anglers looking for a challenge, these trico hatches can serve up some unique sight-fishing opportunities.
Because grasshoppers, crickets, ants, and beetles become active later in the day, beginning the day with a two-fly weighted nymph rig makes the most sense. Choose two small weighted nymphs, such as a size 16 or 18 Pheasant Tail and a size 16 or 18 caddis pupae.
Hatches of evening caddis can be very prolific on the Smith River in August, and anglers willing to fish into darkness can find success. However, this is assuming access can be gained through permission from a private landowner—which is rare—or using a craft capable of floating the Smith River during a month synonymous with very low streamflows.
Where to find August trout on the Smith River
Caddis, stonefly, and mayfly nymphs are active on the Smith River throughout August. However due to water temperatures in excess of 68 degrees F, hatches are often sparse in comparison to earlier in the summer. When water temperatures rise above 68 degrees F, trout will slow their feeding and seek out refuge in classic cool water lies: deep water in pools or runs, fast water riffles, or any place that provides cover from predators, warm water, or bright sunlight.
Even in the deep canyon of the Smith River, bright sunlight penetrates into the water. When the sun becomes high in the sky and sunlight shines into the water, trout will move to cooler holding lies, occasionally moving to feed on a nymph floating by in the current. This direct sunlight on the water paired with rising water temperatures creates unfavorable conditions for hatches and rising trout.
If water temperatures remain below 68 degrees F, trout may seek out terrestrials that have fallen into the river. If this does occur, trout will emerge from cooler water trout lies and intercept a floating terrestrial.
Important August hatches
August on the Smith River is not considered a prime month. Compared to late May and all of June, August is a distant second fiddle to the cornucopia of prolific hatches of early summer. But, because the Smith River is a healthy river and has an abundance of aquatic insect life, hatches in August provide some food for trout.
Terrestrials—insects that live the entirety of their life on land—provide a large portion of a Smith River trout’s diet in August. Spruce moths, 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.
A variety of caddis species ranging in size from 10 to 20 live in the Smith River and hatch throughout the month, occurring at various times throughout the day. Trico mayflies hatch in August on the Smith 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.
Smith River fly box for August
Stonefly nymphs in brown and black in sizes 8 through 10
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;
Grasshoppers in sizes 6 to 10.
Trico mayfly adults and spinners in sizes 18 through 22
Sculpin patterns in sizes 2 to 6
Streamers in olive, black or brown in sizes 2 to 6