How to Choose the Right Flies for Spring Fly Fishing (Complete Hatch-Based Guide)

Spring is a challenging time to fly fish for many anglers. Hatches and strategy can be confusing. In addition to rising water temps, runoff plays a major role in the ecosystem of a river and fishing strategy. Plus, spring brings a variety of hatches, making the fly selection much less straightforward than winter hatches.

Warming water temperatures do bring fish out of winter lethargy and this dramatic switch from winter trout. Spring marks a transition to more aggressive trout behavior.

Most fly fishermen make the mistake of choosing the wrong fly patterns for the incorrect stage of spring fly fishing conditions.

Choosing the right flies in spring isn’t about one magic pattern. It’s about understanding water temperature, hatch progression, and trout metabolism — then adjusting your fly box accordingly.

Let’s break it down step by step.

1. Understand What Spring Does to Trout

If you are new to fly fishing, then read my other blog post on How to Fly Fish Winter. Winter trout have the slowest of metabolisms. Trout are not willing to move to eat and will enter into a lethargic state for most of the winter months. Rainbow trout, brown trout, and cutthroat trout all find the deepest, slowest water to spend most of the cold winter months in.

Spring weather signifies a dramatic transition, and fish are preparing for the spawn and summer hatches.

• Water temperatures begin climbing out of the 30s and low 40s. 

• Trout metabolism increases.

• Insect life becomes active again.

• Pre-spawn and post-spawn movements occur depending on region.

Early spring, the month of March, is still very similar to fly fishing in the winter months. That being that trout are still lethargic. Their main goal is to conserve energy. Once ambient air temperature reaches into the 50s and mid-30s at night, the warmer temperatures of spring fly fishing have arrived.

Warm temperatures are a signal to trout that it is time to start feeding aggressively in preparation for spring runoff and high water living.

Choose a fly that mirrors this weather and water progression.

2. Early Spring: Think Small and Subtle

For early spring fly fishing scenarios, think in a similar way to fly fishing during the winter months. Small flies and minimal hatches will still be encountered on most days. Midges and Blue Winged Olives are going to be your primary aquatic insects that you are going to encounter on the river.

While snow storms are still present throughout the season, watch the temperature gauge. Swings in air temperature are ideal. Whether cloudy or sunny, when the thermometer rises above 32 degrees Fahrenheit, this is the optimal time to hit the river.

Similar to winter, there is no rush to hit the water. Mid-day fly fishing is going to be the best time to begin fly fishing for spring trout. Earlier in the day, fish deep under a strike indicator with midge larva patterns and Blue Winged Olive nymph fly patterns.

As water temperatures rise, continue to fly fish deep with nymph flies, but switch to emerger nymph fly patterns.

Mid-day is the perfect opportunity to nymph deep and then utilize a swing at the end of a dead drift. Swinging flies in this manner simulates the emerging phase of aquatic insects rising vertically through the water column.

When water temps sit between 38–45°F, trout are active — but selective.

Focus on:

• Midges (larva and pupa)

• Small Blue-Winged Olives (BWOs)

• RS2 emergers

• Zebra midges

• Rojo midge

• Black Beauty Midge

• Holo Point Midge

• Palomino Midge

• Sparkle Midge 

• CDC Pheasant Tail

• Perdigon

• Spanish Bullet

Key principle: Match size first, color second.

In cold water, trout rarely move far to eat. Your presentation must be precise and natural.

3. Mid-Spring: Match the Mayflies

Wet, cloudy, and miserable weather days are the best for spring fly fishing. While other anglers are at home tying flies, tough weather conditions often provide the best fly fishing opportunities in the spring months.

Warm air temps, moisture, and cloud cover will often facilitate a Blue Winged Olive hatch. A B.W.O. hatch is usually the first real hatch the trout have seen in the new year.

Increased moisture makes it extremely difficult for hatching aquatic insects to develop their wings and take flight from the water. Mayflies stuck on the surface of the river for prolonged periods of time are the perfect targets for winter-starved trout. These conditions can develop some of the best dry fly fishing of the entire year.

Calm tail-outs and soft seams become feeding lanes. Focus your attention downstream of the prime winter holding water that trout have been living in for the past few months. Slow flat water is where rainbow and brown trout will be holding, making easy work of helpless B.W.O.s.

As water temps push into the mid-to-upper 40s, mayfly and caddis activity increases.

Now you’ll see:

• Stronger BWO hatches

• Mother’s Day Caddis hatch

• Early March Browns (region dependent)

• Increased emerger activity

Must-have patterns:

• Parachute Adams (versatile search dry)

• BWO Comparadun

• Pheasant Tail nymph

• Soft hackle emergers

Emergers are often more effective than full dun or adult caddis patterns in spring because trout key in just below the surface film. Insects stuck in the surface film or struggling to break through the meniscus are easy targets for feeding trout.

If you’re seeing refusals to dries, drop an emerger 12–18 inches below a standard dry fly. Use the front fly as a point of reference to where your emerger pattern is. The rear emerger fly will usually be un-seeable. If a trout porpoises anywhere within a foot or two of your first fly, set the hook.

4. Skwala & Early Stonefly Opportunities

The biggest insects of the year will make their appearance in May or early June. Stoneflies and salmonflies will start to migrate to the banks of the river when the water temperature reaches 55 degrees.

Optimal hatching temperatures truly depend on a variety of factors, so these large stoneflies can hatch anywhere from May to July. This is largely dependent on regional influences. My advice is always to show up and fish what the river gives you. Planning a fly fishing trip based on hatches is usually setting yourself up for failure.

If you are lucky enough to time the salmonfly and stonefly hatch just right, then focus your angling effort on the banks. Stoneflies and salmonflies migrate from mid-river cover to the banks. Nymph fishing under an indicator with a large Pat’s Rubber Legs can produce some of the largest fish of the season.

Use a bright orange strike indicator when nymphing this time of year. If fish come up to look at the indicator, then that is a telltale sign that it might be time to fish large foam fly patterns.

Stoneflies mate in streamside grass. Not all banks will fish hot, so make sure you pick streamside vegetation with a plethora of bugs in the grass. Shorten a heavier leader to 7.5 feet in length. A short leader allows you to make tight, controlled casts deep into cover along the bank. If you aren’t losing some flies into cover, then you aren’t fishing close enough to the banks. That’s how tight you need to cast to the banks.

Large foam flies like G’s Supa Fly, Chubby Chernobyl, Water Walkers, and large stimulators tied in bright orange are all solid flies. The Sofa Pillow is also an old but effective salmonfly pattern.

In many Western rivers, early spring means Skwala stoneflies. These bugs crawl to shore before hatching, which changes trout positioning.

Key adjustments:

• Fish tight to banks.

• Target slow edges near structure.

• Expect aggressive eats.

Effective flies:

• Skwala dry patterns

• Chubby Chernobyl variations

• Rubber-leg stonefly nymphs

• Pat’s Rubber Legs

A dry-dropper setup works extremely well during this window.

Spring is one of the few times large dries produce consistently before summer.

5. Caddis Begin to Appear

In addition to mayfly hatches, the first real caddis hatch will appear. On many rivers in the West, like the Arkansas River in Colorado, the Mother’s Day Caddis hatch is an epic fly fishing experience.

They are called the Mother’s Day Caddis because they hatch around Mother’s Day in May. Millions of small black caddis hatch in clouds, and this will often bring pods of rising fish to the surface. Having a variety of caddis larva, caddis pupa, caddis emerger, and adult caddis fly patterns in the fly box is essential.

One of my favorite tactics when fishing the Mother’s Day Caddis hatch is to twitch and skitter a black Elk Hair Caddis pattern across the surface of the river. This can often induce explosive strikes. Skating and twitching flies is also helpful when the surface of the river is covered in natural insects. This can help bring attention to your fly pattern.

With increased insect activity, it is important to differentiate between trout taking naturals on the surface and trout eating emergers just below the surface film. Distinguishing between the two behaviors is done by recognizing a trout’s rise form.

Porpoising trout are distinguished by having only their dorsal fin and back visible. This behavior is similar to a dolphin porpoising in the bay. Porpoising is a telltale sign that you should throw an emerger pattern that sits just in the surface film of the river. Patterns like an X-Caddis, Klinkhammer, or CDC B.W.O. emerger are all deadly options.

When you see a trout’s entire mouth come out of the water, then that means the trout are eating duns on the surface. Choose a proper dry fly pattern: Elk Hair Caddis, Parachute Adams, Griffith’s Gnat, or comparadun-style flies.

During this phase of the spring fly fishing season, you could encounter midges, caddis, or mayflies. If all three are on the water, start with a fly that matches the most abundant aquatic insect.

As temperatures approach 50°F and beyond, caddis activity increases.

Unlike mayflies, caddis move erratically — which can trigger aggressive strikes.

Carry:

• Elk Hair Caddis

• X-Caddis

• Caddis pupa patterns

• Soft hackle caddis emergers

During heavy caddis activity, trout often key on pupa rising to the surface rather than fully hatched adults.

Swinging a soft hackle can be deadly.

6. When Runoff Hits: Go Bigger & Dirtier

Runoff is always a tough time to fly fish. You can still be successful in high, dirty water. In some ways, high water can make the fishing easier.

Trout have to hold in manageable water that isn’t too fast to survive. Similar to winter fly fishing, large groups of trout will congregate in the little water that is suitable for survival. I like to look for fish tight to the banks, downstream of islands, or downstream of structure. Wide, deep flats with slow water close to banks can hold tons of fish.

Remember trout don’t need to see to eat. Rainbow trout, brown trout, and cutthroat trout all use their lateral lines to sense food. For this reason, fish large fly patterns in the nymph category of flies. I personally like hot pink Squirmy Worms, large egg patterns, and large salmonfly patterns with a hot-spot bead head. All pink Sparkle Worms can also be very effective during runoff.

Spring runoff changes everything.

As water rises and clarity drops:

• Visibility decreases.

• Trout rely more on silhouette and vibration.

• Fish often hold tight to structure.

Switch to:

• Streamers (olive, black, natural tones)

• Woolly Buggers

• Larger stonefly nymphs

• Darker profiles

• Slight flash for visibility

When water is off-color, trout are less selective — but you must get flies close to holding water.

7. Let Water Temperature Guide Your Fly Box

Water temperature is your best decision-making tool.  Carry a thermometer and make adjustments based on water temps.  In the spring, the water temperature will guide anglers in the correct direction on what insects are most likely to be present.  

Here’s a simple spring breakdown:

• 38–42°F → Midges dominate

• 42–48°F → BWOs increase

• 48–55°F → Mayflies + early caddis

• 50°F+ → Streamers and larger profiles become effective

Carry a thermometer. It removes guesswork.

8. Adjust Presentation Before Changing Flies

Spring trout can be inconsistent. Remember, hatches are still variable and sporadic in the spring especially in early spring.  Prior to changing fly patterns, change you indicator depth and weight.  While a trout’s metabolism is increasing with intensity, they may still be lethargic.  

A trout’s strike window can still be relatively small, micro adjustments with you indicator and split shot can make a huge difference in the number of fish catching opportunities.  

Before swapping patterns:

• Change depth.

• Adjust drift speed.

• Try an emerger.

• Lengthen your tippet.

• Move your casting angle.

Often the fly is right — the drift isn’t.

Final Thoughts: Spring Rewards Observation

Spring can be a difficult time for fly fishing. Trying to discern what hatch is occurring, the behavior of trout in various water conditions and clarity, and selecting fly patterns that are effective can be confusing to anglers.

Let the seasons and water temperatures guide your fly choice and fly fishing strategy. Early-season angling can be similar to winter fly fishing. As the water warms, expect to see the first real hatches of the fly fishing season: caddis, stoneflies, and mayflies.

These first hatches usher in some of the best fly fishing before spring runoff. Once runoff occurs, this is an excellent opportunity to fish large fly patterns like worms and eggs.

Spring fly fishing is about progression.

The season moves from subtle and small to active and aggressive.

If you:

• Watch water temperature

• Pay attention to hatch timing

• Match size first

• Adjust to clarity changes

• Stay flexible with presentation

You’ll consistently choose the right flies.

Spring is a season of transition — and when you understand that rhythm, your fly selection becomes intentional instead of reactive.

Master spring fly choice, and you’ll start the season ahead of the curve.