August Fishing on the Ruby River

August weather, stream flows, and summary

Fly fishing the Ruby River in August is unlike many other rivers in Montana. Because the river has two distinct sections, anglers will usually find stream flows and water temperatures favorable for feeding trout. During August the Ruby River is ideally suited for the walking-and-wading angler…if only more of the river were accessible.

In both sections of the Ruby River—upstream of Ruby Reservoir and downstream of Ruby Reservoir—public access points are limited. And when access is obtained through a public access site, anglers must be very considerate of Montana’s access law because landowners are diligent in ensuring anglers do not trespass. The only section where anglers can feel confident in their ability to cover all the water without the risk of breaking the law is the river in Beaverhead-Deer Lodge National Forest. In this section, rambunctious and plentiful trout averaging 10” to 12” make for a fun day of fishing. 

Below Ruby Reservoir, the river twists and turns for nearly 50 miles through hay fields and thick willow-swamped wetlands. This section offers some of the most difficult access imaginable with landowners ready to harass and arrest anglers at any given chance. Limited fishing pressure provides excellent streamer fishing even during hot sunny days. 

August weather on the Ruby 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 75 degrees F. This drop in temperature is helpful for fish. Less than 1” of rain falls throughout the month of August. 

With stream flows typically well below 200 cubic feet per second (cfs) anglers can fish a small, trout-filled river that is in prime condition. However, very little public access combined with the nature of the river itself—abundant deep bends and deep holes and thick bank-side brush cover—make it very difficult to walk-and-wade fish the Ruby River without stepping onto private property. 

August fishing: what to expect

Because floating and fishing on the Ruby River is very difficult, if not impossible for most of the year, August may be one of the best months of the year to fish the Ruby River. As a walk-and-wade fishery, stream flows in August are low enough that adventurous anglers can venture far from any public access site. 

That being the case, other than the section of river in Beaverhead-Deer Lodge National Forest, very little public access exists on the Ruby River upstream of Ruby Reservoir. Below Ruby Dam, several public access sites exist, but walking-and-wading anglers need to be prepared to stay within the public waterway—below the mean high-water level—and be prepared to wade deep, sometimes chest or neck deep to ensure trespassing is avoided. When walking-and-wading the Ruby River, to be confident in avoiding trespassing or avoiding conflict, it is a good idea to always keep your feet in the water.  

When fishing the Ruby River in August, bright sunshine is common. If trout on the Ruby River are to feed on the surface in August, they most likely will do it early in the morning and late in the evening. As the sun rises and penetrates deeper into the water, expect trout to retreat to cool, deep water and cease feeding until the angle of the sun becomes less penetrating. 

Pale Morning Dun (PMDs) mayflies, caddis, and midges 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 Ruby 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, beetles, and spruce moths 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. 

As the riverside grasses warm or an afternoon breeze increases, more terrestrials may land on the water. Spruce moths can also hatch, but only on the uppermost reaches of the river that lie in Beaverhead-Deer Lodge National Forest. 

Hatches of caddis in the evenings can be very prolific on the Ruby River in August, and anglers willing to fish into darkness can find success.  

Where to find August trout on the Ruby River

Caddis and mayfly nymphs, as well as midges are active on the Ruby River throughout August. Brown trout, which dominate the trout population below Ruby Reservoir are less active in August than they may be in late June, July, or in the fall. However, because the Ruby River has plenty of food, paired trout still seek out food in August. 

On the Ruby River upstream and downstream of Ruby Reservoir, terrestrials make up a large portion of a trout’s diet during August. Grasshoppers, ants, spruce moths, beetles, and crickets can all be blown into the river. To fish terrestrials on the Ruby River target the usual holding lies—soft water near fast water, the drop off below a shelf, undercut or shade-covered banks, near the bottom of a deep run, or slow water behind structure. Trout will move out of a holding lie to gobble-up a well-presented grasshopper. 

Because hatches are less consistent in August than in July, finding trout on the Ruby River in August is about finding food and cold water. Unless a strong hatch of caddis, tricos, Pale Morning Dun mayflies, or spruce moths occur—mainly in the uppermost sections—trout can be found in classic subsurface lies: deeper water near shallow water, behind or in front of structure, or any place that provides cover from predators or bright sunlight. 

Important August hatches

Because the Ruby River is a healthy river and has an abundance of aquatic insect life, hatches in August provide some food for trout. 

A variety of caddis species live in the Ruby River and can hatch in August, occurring at various times throughout the day. Most caddis species in the Ruby River are size 14 to 18. During August, hatches of tan or black caddis can occur in the evening hours, creating a special hour or so of fishing. These caddis are size 18. 

Trico mayflies are small mayflies—sizes 18 through 22—and hatch in the early morning hours on the Ruby River. 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 on land—provide a large portion of a Ruby River trout’s diet in August. Grasshopper, crickets, ants, beetles, spiders, spruce moths, and any other land-dwelling insect that may end up floating in the river’s current can end up as trout food. Hatches of spruce moths are limited to the section of the Ruby River upstream of Ruby Reservoir, with the bulk of spruce moths hatching on the section of river in Beaverhead-Deer Lodge National Forest. 

A few sporadic Pale Morning Dun (PMDs) mayflies can emerge on the Ruby River in August. Primarily downstream of Ruby Dam, PMDs may hatch between 9 AM and noon. As the sun rises and sunlight penetrates deeper into the water, the hatch will wane. 

Ruby River fly box for August

Caddis pupae size 12 to 18

Caddis CDC emergers size 12 to 18

Caddis dry flies with dark grey, black or brown bodies in size 12 to 18; 

Grasshoppers in sizes 6 to 10

Trico mayfly adults and spinners in sizes 18 through 22

Spruce moths in size 16

PMD nymphs in sizes 16 or 18

PMD emergers in sizes 16 or 18

PMD dry flies in sizes 16 or 18

Stonefly nymphs in brown and black in sizes 8 through 10

Sculpin patterns in sizes 2 to 6

Streamers in olive, black or brown in sizes 2 to 6