Springtime Rocky Mountain Tailwaters

October 05, 2011 By Ross Purnell, Editor

If you are in search of pre-runoff spring dry-fly fishing in the Rocky Mountain West, you have two options: freestone or Rocky Mountain tailwaters. Freestone streams offer some opportunities to cast drys to rising trout, but fishing conditions are unpredictable at best. Prior to runoff, freestones can turn into chocolate milk overnight with excessive rain or snowmelt, and cold weather can delay hatches for weeks. Tailwaters, on the other hand, are rarely affected by weather and are more dependable during the early season because they have constant, regulated flows and stable water temperatures. You can count on tailwater hatches to provide excellent springtime dry-fly fishing.

Tailwater fisheries receive water from immense reservoirs through manmade dams. This water, often full of nutrients and oxygen, supports a healthy environment for aquatic insects and vegetation below the dam. It allows trout to eat year-round and grow quickly. The stream's water conditions are managed by annual water trends and scheduled water releases, not the vagaries of daily weather patterns. Water conditions such as clarity, level, and temperature remain relatively constant year-round, and provide important habitat for insects. Early-spring Blue-winged Olive (Baetis, BWO) and midge hatches are often intense and offer the best dry-fly fishing of the year.

The Green River

Like other well-known Western tailwaters, Utah's Green River flows clear and nutrient-rich from a manmade impoundment. Unique to the Green is an apparatus on the Flaming Gorge Dam that allows dam operators to draw water from whatever level of the reservoir is most conducive to recreation. For fly fishers, this translates directly into fantastic early-spring nymph and dry-fly fishing.

In early April, when the surface water of the reservoir begins to warm, dam operators open the outlet gates close to the reservoir's surface (40 feet under) and release water into the river. The slightly warmer water temperatures trigger the first heavy mayfly hatches of the spring, and the big rainbows and browns start to eat intensively.

The main event on the Green is the afternoon Blue-winged Olive hatch. The BWOs begin sporadically in late March and become more common as the water warms in April. By the last week in April, BWOs cover the water almost every afternoon. The heaviest hatches continue well into May, then dwindle. Unless it's an unusually cool, wet spring, the hatch is over by June.

The first BWOs of the year are a #16, and as the hatch progresses, duns become smaller. Although #18 is by far the most common size, you'll see a few duns in late May best matched with a #20.

Overcast days trigger the heaviest BWO hatches and encourage fish to feed on the surface. On such days, a thick, late-morning midge hatch is an indicator that an afternoon BWO hatch is on the way, as both insects prefer overcast conditions. In the afternoon, be prepared for some great dry-fly action for big fish. Look for large trout poking their noses out along foam lines and porpoising on the flats.

When fishing the Green or other tailwaters in spring, there is a chance you'll witness a BWO blanket hatch. While an amazing spectacle, it can also be the most frustrating. Blue-winged Olive duns become so thick on the surface, and the trout become so focused and selective, that your fly gets lost in the shuffle. With hundreds of food items passing over a fish at any given time, the chances of your fly getting noticed are slim. When this happens, try to measure the trout's feeding rhythm and present your fly in the fish's window just before the next rise.

Dennis Breer of Trout Creek Flies ([800] 835-4551) says effective BWO patterns include low-riding, flush-in-the-film flies like a Parachute Adams or BWO Sparkle Dun (#16-#20). For midges, he uses a Parachute Adams, Fuzzball, or a Griffith's Gnat (#18-#20).

The Colorado's midges hatch 365 days a year, but they are relatively sparse during the winter months. Winter nymph fishing is excellent, but you'll rarely see fish on the surface. Around March 1, however, the sun gains enough elevation to pierce the dark depths of Glen Canyon, and almost as soon as the sun hits the water, the midge hatch kicks into high gear.

The Colorado's midge hatch is a marathon event. Springtime hatches can last all day and provide you with a shot at 100 or more hookups a day.

Terry Gunn of Lees Ferry Anglers ([800] 962-9755) recommends #20-#24 dry-fly patterns to imitate single midges, and #18 Griffith's Gnats to imitate midge clusters (clumps of midges balled up together). Parachute Adams and Royal Wulff drys (#18) also take plenty of fish. Midges are most vulnerable to the trout as they transform from pupa to adult, and either a small Zebra Nymph fished deep or a Trailing-Husk Midge fished in the surface film is deadly.

During the heavy midge hatches of March, April, and May, low water levels create plenty of shallow areas for easy wade fishing and good sight fishing to large trout. The best dry-fly fishing of the year and the heaviest midge hatches disappear with the high water in June.

Bighorn River

Montana's Bighorn River below Yellowtail Dam is a wide, shallow river that runs through the grasslands of eastern Montana. The Bighorn's hatches are legendary and its spring emergences are no exception. Midges hatch on the Bighorn all winter, but in March when the winter ice breaks away and water temperatures rise to about 40 degrees F., the hatches intensify.

At first, the dry-fly fishing is limited. It's mostly nymph and streamer fishing in the morning, with a chance at some surface activity in the afternoon. If the afternoon hatch is on, big rainbow- and brown-trout snouts appear along the edges and in slow current seams. Trout are sluggish early in the season and won't expend a lot of energy for a single midge. Look for them in extremely slow and sometimes shallow water, for example on the inside of a long sweeping bend. You'll rarely find big fish in fast riffles during the early season, except for spawning rainbows, which should be avoided.

In April, the midge hatch turns from a midday affair to an all-day event, with the hatch peaking after lunch. Overcast, miserable days bring out the best hatches, and midge clusters are more common. Bighorn trout can't resist these morsels, and instead of the sporadic dry-fly fishing you find earlier in the year, you'll find pods of rising trout working the flats, finning in the shallows, and feeding along the bank.

Hale Harris of Big Horn Trout Shop ([406] 666-2375) says a Griffith's Gnat works well to imitate midge clusters, but he prefers his CDC Midge Cluster that floats high on the water's surface. Adult midges and midge clusters don't break the water's surface, so your pattern should be light and float only on its hackle points.

By the third week in April, the spring BWO hatch begins. On many afternoons, you'll find tiny mayflies (#20) and a blizzard of midges on the water. Though the BWOs aren't much bigger than the midges, trout seem to prefer them. A #20 Parachute Adams is a good mayfly and midge-cluster imitation.

Presentation is 90 percent of the early-season puzzle; make sure you present your flies dead-drift. If current changes cause microdrag on your leader, trout will refuse your offering without an obvious explanation. Try casting from a different position, or try a different cast (one that will put more slack into the leader) before you tie on a new fly.

Missouri River

Spring on Montana's Missouri River below Holter Dam (near Helena) is similar to the Bighorn. Midges hatch all winter and then explode in massive emergences on cloudy days in March, April, and May. BWOs appear in April and continue until late May when high water washes away the best dry-fly fishing.

Missouri River guide Neale Streeks ([800] 800-8218) says a Parachute Adams works on 90 percent of the river's browns and rainbows. His version has a black (instead of white) calftail wing for better visibility on dark, overcast days. You can also use a slightly larger fly (#16) for better visibility. Although most of the early-season BWOs on the Missouri are about a #18, the trout are not as finicky in the spring as they are later in the year.

South Platte River

Colorado's South Platte is so punctuated with dams and reservoirs it's hard to call it a river. The great fishing is concentrated between Spinney Mountain Reservoir and Elevenmile Reservoir (3 miles); downstream from Elevenmile Reservoir in Elevenmile Canyon (3 miles); downstream from Cheesman Reservoir in Cheesman Canyon (3 miles); and in the public water near the town of Deckers (13 miles).

BWOs are the most important mayfly on the South Platte, and the spring hatches trigger some of the best dry-fly fishing of the season. The hatch begins in March and lasts into May, with the best hatches coming on miserable days in April. If snow is in the forecast, plan to miss work. Snow can trigger fantastic BWO hatches.

The South Platte's BWOs are incredibly small. A "big" fly is a #20 and you will probably need a #22 (or smaller) Parachute BWO to match the hatch. The rainbows and browns are extremely leader-shy, so use a 6X tippet and always try to position yourself for a down-and-across presentation to risers. This is not a chuck-and-chance-it fishery, and you'll be most successful if you take the time to make the right presentation.

San Juan River

New Mexico's San Juan River below Navajo Dam is one of the most popular tailwaters in the West. BWOs can hatch any day of the year. March and April are the best spring months for dry-fly fishing. In May, dam operators release an artificial "flush" of water to benefit several endangered fish species, and the surface activity cools down. (Normal flows in March and April are 500 cfs; in May, flows are as high as 5,000 cfs.)

The San Juan's BWO hatches start in mid-morning and the rainbows begin working the surface shortly after. Watch feeding trout closely to determine what stage of insect they are eating. If they are taking surface-riding duns, their noses will clearly break the surface and close over the mayfly. Watch the duns to see if any actually disappear into the fish's maw. If the fish are taking emerging nymphs just under the surface film, you'll see only swirls and the backs of trout.

When the fish are on emergers, use an unweighted #22 Pheasant-tail Nymph or an RS2. Try your fly with and without floatant. Later in the hatch, especially if the hatch is heavy, the fish focus on duns. A #20 CDC Compara-dun or #22 Sparkle Dun will be your best fly choice.

Tailwaters give us the chance to cure the winter blues and get out the floating line and dry-fly box. The rivers mentioned above are only a few of the choices available for excellent spring dry-fly fishing. The Provo River (near Provo, Utah) and the Frying Pan River (near Basalt, Colorado) also have good BWO and midge hatches, and the fishing for big fish is superb.

Ross Purnell is the Web Content Director for the Virtual Flyshop, www.flyshop.com. He lives in Fort Collins, Colorado.