August Fishing on the Madison River

August weather, stream flows, and summary

August fly fishing on the Madison River can feel very similar to July and it can be quite different than July. Early in August the weather is similar to July and later in the month, the weather is similar to September with cool mornings and evenings. Hatches of aquatic insects—PMDs, caddis, and stoneflies—are less prolific than July, but grasshoppers, ants, beetles, and spruce moths provide plenty of available food for trout. 

During August on the Madison River there are less than five days with measurable precipitation. Temperatures early in the month average in the high-80s and later in the month dip to the low 80s. From early morning nymphing to afternoon prospecting with grasshoppers to the hope of an abundant hatch of spruce moths, fly fishing the Madison River in August can be exciting. 

Stream flows run consistent and clear throughout the month, but fishing the Madison River in August requires an understanding of how water temperatures affect hatches and feeding fish. Early August features plenty of long, sun-filled days and fishing action and hatches are similar to July. While wonderful for suntans and flip-flops, prolonged high air temperatures and bright sun does affect the habits of trout and hatches. 

In early August as water temperatures climb past 62 degrees, hatches of Pale Morning Dun mayflies subside. With the lack of a prolific hatch, trout on the Madison River become more opportunistic…and August becomes the month of fishing terrestrials—grasshoppers, ants, beetles, and spruce moths. 

An important yet overlooked factor of August is that the nightly low temperature in late August are almost five degrees F cooler than earlier in the month. Additionally, by the end of the third week of August there is one less hour of daylight. Many anglers think late-August is a time to forego fishing the Madison River altogether, however these slight changes can make a big difference for active trout later in the month.

August fishing: what to expect

August fly fishing on the Madison River can feel like a river of split personalities. Some days a strong emergence of PMDs can occur and trout will be actively feeding on nymphs, emerging adults, and fully hatched adults on the surface. Other days will be absent of PMD hatches and the river seems quiet of aquatic-based insect life. However, the prospect of trout feeding on grasshoppers, ants, or beetles is always high and because terrestrials make up a good portion of a Madison River trout’s diet in August, the likelihood of some exciting dry fly fishing always exists.

A typical August day fly fishing the Madison starts early, often before sunrise. Because the bright sun and warmer temperatures of August are the norm, the best times to fish the Madison River in August are from daybreak to early Afternoon. If an abundance of terrestrials land in the water and the Madison River’s trout continue to feed, there can be exceptions to starting early and ceasing fishing in the afternoon. When terrestrials land on the water fishing in the afternoon can be quite good. 

Because grasshoppers, ants, and beetles become active later in the day, beginning the day with a two-fly weighted nymph rig makes the most sense. Even though the stonefly hatches of June and July are over, choosing a stonefly nymph is a good idea because stonefly nymphs are active in the Madison River year-round. 

PMD and caddis nymphs are active year-round as well, so a stonefly nymph and a mayfly or caddis nymph are the go-to choices for prospecting with a two-fly weighted nymph rig in August. Trophy trout-seeking anglers can also start at dawn and drag, swing, or slowly strip a large streamer pattern and might entice a big trout. 

As the sun rises during mid-day, grasshoppers, ants, and beetles become more active. Choosing to fish a two-fly grasshopper and an ant pattern together—yes, two dry flies at the same time—is a successful tactic on the Madison River in August. If the wind begins to blow, which is common on the Madison, more terrestrials may blow into the river enticing even more trout to be opportunistic feeders. 

More-so in some years than others, spruce moths hatch from bank-side pine trees. These light-colored moths can hatch at any time during the day and may find themselves floating on the water’s surface. These moths mostly hatch on the river upstream of Ruby Creek. Unlike the predictability of a PMD hatch, a hatch of spruce moths is very sporadic. But when they do hatch and land on the water, the Madison River’s trout aggressively feed on these caddis-like moths. 

Where to find August trout on the Madison

Finding trout on the Madison River in August is the result of educated prospecting. As each day is different, understanding external environmental factors is important. Because the reliability of a consistent hatch is unlikely in August, trout on the Madison River in August will, or will not, follow the food. 

Mayfly, caddis, and stonefly nymphs are active year-round on the Madison River. In August trout may simply stay put, sitting in subsurface holding lies occasionally feeding on a nymph floating in the current. These trout will be found in classic holding lies: deeper water near shallow water; behind or in front of structure; or any place that can provide cover from predators or fast currents. 

Sunlight also plays a role in where trout are found on the Madison River in August. In early morning or late evening hours, trout may feed in shallow water. As the sun rises these trout most likely move to deeper water, the darkness of the deep water providing cover from overhead predators. 

So...what food source can entice trout out of these holding lies or from the deeper water? Grasshoppers, ants, and beetles, that’s what. Most grasshoppers are large—ranging in size from 4 to 14—and that size is large enough to entice a trout to swim to the surface to eat. Trout will expend vital energy and take the risk from deep cover because a morsel as large as a grasshopper, ant, or beetle may not pass by again that day. 

Important August hatches

Fly fishing the Madison River in early August is similar to July: hatches of PMDs in the morning and caddis in the evening. Unlike July, the hatches are much smaller in frequency and less reliable. Trico mayflies can also be spotted, but in the Madison River’s fast currents they usually go untouched by any hungry trout. 

The highlight hatch of August on the Madison River isn’t really a hatch. Terrestrials—insects that live the entirety of their life on land—make-up a large portion of a Madison River trout’s August diet. Grasshoppers, ants, spruce moths, beetles, spiders, crickets, and any other land-dwelling insect that may inadvertently find its way into the river could end up as trout food. 

Madison River fly box for August

PMD nymphs sizes 12 to 18

PMD emergers sizes 12 to 18

PMD dry flies sizes 12 to 16

Grasshoppers in sizes 6 to 12

Ants in brown, cinnamon, and black in sizes 12 to 20

Beetles in black in sizes 10 to 18

Spruce moths in sizes 12 to 16

Stonefly nymphs in brown and black in sizes 4 to 10

Caddis pupae sizes 14 to 16

Caddis CDC emergers sizes 14 to 16

Caddis dry flies with dark grey, black or brown bodies in sizes 14 and 16; 

Crayfish patterns in sizes 2 to 8

Sculpin patterns in sizes 2 to 6

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