August Fishing on the Montana Spring Creeks

August weather, stream flows, and summary
August on Nelson’s, DePuy’s, and Armstrong’s spring creeks serve up the least crowded weeks of the summer angling season. Like late June and early July, it is not a secret about the great fishing during this timeframe with prolific hatches of Pale Morning Dun (PMDs) and sulfur mayflies. But it is also not a secret about the lack of hatches and rather inconsistent fishing on the creeks in August. 

Despite hatches that are less frequent and less strong, many of the same fish are in the spring creeks in August, the fish just have less food from which to choose. Add to the equation, days and weeks of prolonged sunshine, and many spring creek trout simply retreat to deeper water to avoid exposure to possible overhead predators. But…trout still need to eat and that’s why fly fishing the spring creeks in August is never a bad idea. 

During August on the spring creeks there are less than four days with measurable precipitation, averaging slightly less precipitation than July. Daily high temperatures during the first two weeks of August average well above 80 degrees F dropping to 78 degrees F by month’s end. The potential exists for daytime highs in the mid to upper 90 degrees F as well. This all shapes up to less than ideal conditions for strong emergences of PMDs or sulfurs, but for plenty of active terrestrials. 

Unlike late June and early July’s difficulty in finding availability—the creeks are on private property and a rod fee and reservation is required—getting a day on the spring creeks in August is rarely a problem. This abundance of availability illustrates the lack of match-the-hatch dry fly opportunities compared to earlier in summer. However, with less people and just as many trout, for anglers willing to think—and fish—outside of the typical spring creek fly fishing norms, August on the spring creeks serves up some solitude and challenging fishing opportunities. 

August fishing: what to expect
It is important to understand that any angler fishing Nelson’s, DePuy’s, or Armstrong’s spring creek in August should immediately lower their expectations IF they are comparing the opportunities to June, July, or even April or May. Why? The answer is simple: because August doesn’t have the preponderance of strong hatches that occur in the earlier summer and spring months. This doesn’t mean fishing is poor, but it does mean the fishing action is slower.

On a typical day of fly fishing the spring creeks in August, anglers can expect sporadic hatches, if any. Pale Morning Dun (PMD) or sulfur mayflies have all but ceased. Hatches of caddis will be restricted to the evening hours only, but the potential exists for an hour or two of great fishing with long leaders and size 18 to 20 dry flies during the “golden hour” just before sunset. To round out the hatches for August, tricos may emerge inconsistently in the early morning hours. 

If tricos hatch, anglers can have a few hours of quality head-hunting to trout sipping spent tricos in seams and riffle corners. Expect to wake up early, aim to be on the water shortly after first light, and fish long leaders and supple tippets with size 18 to 22 trico spinner patterns. 

If hatches are minimal, then trout will feed on terrestrials and midges or mayfly nymphs. For fishing midges and mayfly nymphs in the deeper buckets and holes, long leaders of 12- to 15-feet are best, tapered to 5X or 6X fluorocarbon tippets. A tandem nymph rig on a 12- or 15-foot leader tapered to 5X or 6X fluorocarbon with a size 18 or 20 midge or Pheasant Tail can produce fish. Most experienced spring creek anglers use small yarn or light pinch-on indicators and small size—6 to 12—split shot. Because most currents on the spring creeks run slower than larger rivers, less weight and shorter depths from fly to indicator are essential. Successful patterns include Sawyer Pheasant Tails, Zebra midges, and WD-40s.

For dry fly anglers, terrestrials will provide the bulk of the excitement. But unlike freestone trout who are opportunistic feeders and often are eager to move several feet to gulp a grasshopper, ant, or beetle, spring creek trout have plenty of options for food without having to swim far. Anglers desiring to fish terrestrials on the spring creeks should be patient, expect to cover plenty of water, and always be ready to expect the unexpected because though the spring creeks are full of fish, the fish just may not be full-on ready to eat terrestrials. 

Where to find August trout on Nelson’s, DePuy’s, and Armstrong’s spring creeks
Finding trout on the spring creeks in August requires a little more effort and patience than in June or July. Because hatches are less in volume, diversity, and duration, trout on Nelson’s, DePuy’s, and Armstrong’s spring creeks in August are going to seem more elusive. However, that really isn’t the case. They just don’t move around as much or feed more predictably, but they do not rise and feed on the surface regularly so tandem nymph rigs are the most successful way to find fish in August. 

Because August is at the tail-end of summer, most spring creek trout have become very sensitive to sunlight and hold and feed in deeper, slower water compared to the shallow flats and long runs of June and July. In this deeper, slower water, fish are probably eating midges, scuds, sowbugs, or mayfly nymphs. On the spring creeks “deeper water” is any three to six feet deep depression or bucket that is near a shallow flat or riffle.

Because the spring creeks are loaded with food, any small change in depth or break in current can create a holding lie, which can also be a feeding lie. Target any change in current speed or change in depth, such as a bucket or small depression where the depth may be a foot or so deeper than the nearby bottom structure. 

The spring creeks, because they are surrounded by fields of tall grasses, can have some decent fly fishing with terrestrials in August. As the sun rises and the grasses warm and perhaps a breeze begins, casting a terrestrial into holding and feeding lies can entice a strike. Trout on the spring creeks tend to be more selective and eat on hatching insects rather than opportunistically feeding on whatever passes by, but riffles, shelfs below riffles, seams along banks, or shaded cut-banks are all possible locations where a well-presented grasshopper, ant, or beetle can produce a take.

Important August hatches
August on the spring creeks sees the least prolific hatches of the angling season. This doesn’t mean hatches do not occur in August, as they do. But it does mean the frequency and duration of hatches are considerably less than the fall and summer months. 

Terrestrials—insects that live the entirety of their life on land—may make up the bulk of a trout’s diet in August on the spring creeks. Grasshoppers, crickets, ants, beetles, spiders, and any other land-dwelling insect that may inadvertently find its way onto the surface may be targeted by trout as well. 

Midges are active year-round on the spring creeks and make-up a massive chunk of a trout’s diet. During August, trout may feed almost exclusively on subsurface midges. The lack of other strong hatches and consistent sunshine force a lot of spring creek trout to feed on midges near structure or mostly in deep water. Fishing midge patterns is best done subsurface as part of a weighted two fly rig. 

Pale Morning Duns (PMDs) and sulfur mayflies are almost entirely complete by August. There may be a very few sporadic emergences in early August and again in late August, but they will be random and impossible to predict. 

Trico mayflies hatch in the early morning hours and can also provide opportunities for small fly dry fly fishing. Trout on the spring creeks may 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—and are floating lifeless on the surface. 

Caddis hatches are very sporadic throughout August. If a hatch does occur, it will be strongest in the few hours surrounding evening twilight. Most caddis on the spring creeks are tan or brown and in sizes 16 or 18. 

Strictly subsurface, scuds and sowbugs are often thought of as the same insects, but a scud resembles a freshwater shrimp and a sowbug looks like a “rolli-polli” bug. Especially if hatches of PMDs, sulfurs, or midges are small, a trout on the spring creeks in August may eat a well-presented subsurface scud or sowbug.

Paradise Valley Spring Creeks fly box for August
Grasshoppers, in tan, grey, or yellow, in sizes 10 to 16

Ants, crickets, and beetles in sizes 12 to 18

Midges, especially Zebra midges in black or olive, in sizes 18 through 22

Trico nymphs in sizes 18 to 22

Trico duns/adults in sizes 18 to 22

Trico spinners in sizes 18 to 22

PMD dry flies size 16 to 20

PMD emergers size 16 to 20

PMD nymphs size 16 to 20

Sulfur mayfly dry flies in size 18 to 22

Sulfur mayfly nymphs in size 18 to 22

Sulfur mayfly emergers in size 18 to 22

Caddis pupae size 18 to 22

Caddis CDC emergers size 18 to 22

Caddis dry flies with tan or black bodies in size 18 to 22; 

Scuds in sizes 16 through 20

Sowbugs in sizes 16 through 20