May Fishing on the Montana Spring Creeks

May weather, stream flows, and summary
May on the Paradise Valley Spring Creeks is the tail-end of spring, yet not quite summer, causing it to be a month of transition on Nelson’s, DePuy’s, and Armstrong’s spring creeks. Even though the creeks bubble out of the ground at a constant temperature of approximately 52 degrees, hatches—and the subsequent feeding habits of trout—are still products of external factors like daytime high temperatures, sunshine, wind, and precipitation. 

During May, the daily high temperature is often pleasant with average daily highs in the low 60 degrees F, but by month’s end increases to the low 70 degrees F. Average daily precipitation also increases throughout the month, with the first two weeks of May seeing nearly half the potential of measurable precipitation compared to the last two weeks. It is rare to have snow in May, but there is a good probability for overcast skies, which translates into the strong possibility of thick hatches of Blue Winged Olive (BWOs) mayflies. 

Wind can also dictate the fishing on the spring creeks. If winds exceed 15 MPH many of the hatching dry flies are unable to stay on the water as they get blown off before a trout can consume them. Plus, long leaders that are essential for success are a little more difficult to cast. On windy days, knowledge of the creeks is essential, as plenty of sections exist that may be tucked away or out of the prevailing wind. 

As May lingers on and June approaches, hatches on the spring creeks dwindle. This doesn’t mean that spring creek trout cease feeding, but it does mean the prospect for dry fly fishing tapers and doesn’t reappear until mid-June when Pale Morning Dun (PMDs) mayflies hatch. However, the second half of May on the Paradise Valley Spring Creeks is a sight-nymphers paradise. With an abundance of fish and massive populations of midges, scuds, and sowbugs, anglers desiring shallow water, sight-nymphing opportunities along with a little solitude will be very happy. 

May fishing: what to expect
May on the Paradise Valley Spring Creeks is a unique month. The prospect of strong hatches of Blue Winged Olive (BWOs) mayflies dwindles as the month progresses and caddis hatches in May tend to also be stronger early in May. In most years by the middle of May, the spring creeks are mostly fished with subsurface nymph rigs. Granted, most of that subsurface nymph fishing is still sight fishing—fish are seen feeding near the bottom or suspended in current seams. 

When hatches of BWOs or caddis are prevalent, simply look for rising trout. Fish a leader no less that 12-feet long and use size 6X supple tippet. Most BWOs and caddis on the spring creeks in May are sizes 18 to 22. Dry fly anglers should be armed with supple tippets in sizes 5X and 6X, plenty of quality floatant that works well with CDC, and the ability to execute a reach cast.

A typical day fishing Nelson’s, DePuy’s, or Armstrong’s spring creeks in May often begins fishing a shallow-water, sight-fishing nymph rig with size 18 or 22 midge or mayfly nymphs. Long leaders of 12- to 15-feet are best, tapered to 5X or 6X fluorocarbon tippets. A tandem, shallow water rig on a 12- or 15-foot leader tapered to 5X or 6X fluorocarbon with a size 18 or 20 scud, sowbug or midge 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.

During May anglers desiring to fish streamers may find a little more success compared to April. This is particularly true in DePuy’s and Nelson’s spring creeks. These two creeks flow into the Yellowstone River and trout seeking a respite from the Yellowstone River’s high stream flows in May can migrate into these two spring creeks. Unlike their resident spring creek cousins, these trout may be more opportunistic and chase a streamer. Choose size 4 to 8 sparsely tied, internally weighted streamers in black or olive. 

Where to find May trout Nelson’s, DePuy’s, and Armstrong’s spring creeks
Because trout on the spring creeks in May are going to follow the food, if a hatch of Blue Winged Olive (BWOs) mayflies doesn’t occur, most spring creek trout will be in deeper water. The spring creeks are home to a plethora of available trout food. Because of this, any small change in depth or break in current can create a holding lie, which because of the abundance of food, can also be a feeding lie.

Even if fish are not rising, it is highly likely they are still feeding. 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. Plus, with the crystal clear water of the spring creeks, sight-fishing is a daily occurrence, so be prepared to actively pursue specific fish—it just may be with shallow-water, lightly weighted nymph rigs.

On the spring creeks “deeper water” typically translates into any three to six feet deep depression or bucket that is near a shallow flat or riffle. Because hatches of Blue Winged Olive (BWOs) mayflies are a mid-day hatch, prior to noon or early afternoon, most fish will be found in slower, deeper water and then as a hatch begins the fish will adjust their locations based on the available insects. 

When a strong hatch occurs, look for fish in slow current seams, on shallow flats, a slow seam next to a fast seam, any shallow water adjacent to any deep water, eddy lines, and seams behind rocks or seams created by faster water being slowed down by slow water. 

If a hatch of BWOs is minimal, look for fish to be eating midges. Many of these fish can be seen because the water of the spring creeks is very clear. If fish are spotted and they appear to be active—shifting from side to side and opening their mouth—then a well-presented shallow-water tandem nymph rig may entice feeding fish in these subtle drop-offs below a riffle. 

During May the spring creeks are vital spawning habitat for many Yellowstone River trout. Rainbow trout, Yellowstone cutthroat, and cutthroat-rainbow hybrid trout will migrate from the Yellowstone River to spawn. Be extremely cautious while walking-and-wading and avoid walking on redds or fishing in the vicinity of redds. Additionally, if a spawning or spawned-out trout—skinny, dark in color and has the appearance of looking beat-up and tired— is caught, please release as quickly as possible.

Important May hatches for Nelson’s, DePuy’s, and Armstrong’s spring creek
Hatches of Blue Winged Olive (BWOs) mayflies and caddis can occur in May. BWOs and caddis are the primary hatches of the month. Midges are active year-round on the spring creeks and make-up a massive chunk of a trout’s diet. Fishing midge patterns is best done subsurface as part of a two fly, lightly weighted nymph rig. 

As water temperatures climb above 50 degrees F, these insects can hatch on sunny or cloudy days. BWOs will hatch in abundance on cloudy, rainy days but on sunny days might only hatch in small numbers. Caddis tend to hatch on the spring creek when the water temperatures rise above 55 degrees F. However, compared to the potential of the Mother’s Day caddis hatch on the Yellowstone River, caddis on the spring creeks are minimal at best. 

During May, midges, scuds, sowbugs, aquatic worms, and craneflies are abundant in the spring creeks, with midges accounting for over half of a spring creek trout’s diet. Strictly subsurface, these insects are active throughout May and available to hungry trout. Scuds and sowbugs are not exactly what an angler may think of when it comes to hatches, yet they are a key food source for trout on the spring creeks. 

Paradise Valley Spring Creeks fly box for May
BWO dry flies size 16 to 20

BWO emergers size 16 to 20

BWO nymphs size 16 to 20

Caddis pupae size 14 to 18

Caddis CDC emergers size 14 to 18

Caddis dry flies with dark grey, black or brown bodies in size 14 and 18; 

Scuds in sizes 16 through 20

Sowbugs in sizes 16 through 20

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

Sculpin patterns in sizes 2 to 6

Streamers in olive or brown in sizes 2 to 6