Short answer: match the stage, not just the insect. If fish are sipping and refusing your dry, they're almost certainly taking emergers in the film. Fish a BWO in sizes 18-24 on 5X or 6X, get a genuinely drag-free drift, and go out on the grey drizzly days everyone else skips.

One fly pattern symbolises the beauty and challenge of fly fishing: the Blue Winged Olive. Revered by anglers across the globe, it imitates a mayfly species found in many waters and a critical food source for trout. Imitating miniature sailboats on the water, they come in waves that look like a satellite video of the America's Cup from thousands of feet in the air.

Before you fish them, make sure you can identify them — read Identifying the Blue Winged Olive (BWO) Fly and Hatch first.

Understand the life cycle

BWOs, like all mayflies, have four life stages: nymph, emerger, dun, and spinner. Knowing these stages and when they're most prevalent tells you which pattern to use. For the detail, read Mayfly: Stages of an Insect.

Select the right fly

A best practice is to select patterns in the order of observation, silhouette, size, and colour — then present them well. BWOs generally range from size 18 to 24, though at certain times of year larger (16) or smaller (26) are present. Pay close attention to the naturals on the water and adjust size accordingly.

That order is a formula I use constantly:

• Observation
• Silhouette
• Size
• Color
• Presentation

Learn the OSSCP formula in full here.

Matching the hatch

This is fundamentally sound and used by many. My particular position is that it's significantly more effective when dry fly fishing than when nymphing. Fish are primarily opportunistic feeders and will almost always go after what's available. In many top-water hatch scenarios the food type is so prevalent that it lets them key in on certain characteristics and make decisions rapidly — they know they can feed well, avoid mistakes, and worry less about predators.

So if trout are feeding on emergers, a dry fly pattern won't be as effective. Choose a BWO emerger and fish it just below the surface.

Master the drift

A drag-free drift is crucial, and fishing a BWO is no different. Whether you're using a dry, an emerger, or a nymph, drifting naturally with the current makes all the difference. Presentation, as I said above, is by far the most important element of fly selection.

What that means practically: consider the water type you're fishing, where the fish is feeding, and which fly suits the presentation. Is the fly buoyant enough? Are the currents drowning naturals and are fish eating them subsurface? Are fish eating on top, or taking emergers? Are they on spinners? Are the BWOs they're eating in different phases? Are they floating high or low? Observation determines the characteristics of the fly you choose.

The Sacrificial, Sight, and Feeding Zone formula

• Sacrificial Zone — landing the fly far enough in front of the fish that it isn't yet in their line of vision. Not so far ahead that you line-spook them, but far enough that a short section of the presentation can be sacrificially poor. The aim is to set the fly up so it enters the Sight Zone and exits the Feeding Zone in a perfect drift.
• Sight Zone — where the fly first comes into the fish's view. The presentation has to be right by this stage of the drift, so the fish can act on it without hesitating.
• Feeding Zone — where you believe the fish will eat. Determined through observation, and best thought of as a sphere of opportunity. In all directions, how far will this fish move to feed? Ahead, below, left, right, up, or down.

Technical example: use a wiggle cast to position your line with additional slack between you and the fly. That gives you a drag-free drift for longer, and through the Feeding Zone.

The full breakdown of the three zones is here.

Focus on riffles and runs

BWOs typically hatch in faster-moving water, so focus on riffles and runs. Trout position themselves at the tail end of these faster sections waiting for emergers.

In many cases I'll fish further back, trying to catch a fish and pull it away from the riffle to keep the pod unaware of the disturbance. Then I reset and move forward. On other occasions I'll target the head of the pool — that's determined by the quality of the target fish. If I see one that outweighs the others, I'll often go there first.

Technical tip: given the small size of BWOs, light tippet (5X or 6X) makes your presentation more natural and gives the fly freedom to move in the current. Stock up on 5X tippet and see all tippets.

Adjust to weather

BWO hatches are heavily influenced by weather. Overcast, drizzly days are prime, and those conditions help you too — the natural surface disturbance hides your position and your presentation.

Investing in a quality pair of polarized glasses with a low-light sensitive lens, like yellow, can be the ticket to a great visual day. This is the one piece of gear where spending genuinely changes what you can see.

Don't forget the spinner fall

After mating, BWOs return to the water as spent spinners. These form large mats on the surface and trout feast on them. Observe the water's contents below riffles and in eddies.

When you see masses of spinners floating, it pays to change to a spinner-only dry fly — or one of my favourites, a slightly larger adult dun with a trailing spinner about eighteen inches off the back. The forward fly shows you roughly where the back fly is, and you may get an eat on it too.

Experiment with technique

The traditional dead drift is the go-to, but sometimes imparting a slight twitch or slide to your BWO induces strikes by imitating the struggling motion of the natural. I tend to do this with crippled versions, since they're often more active in the struggle to shed their trailing shuck.

Observe and adjust

Let's recap the observation point. Always pay close attention to the behaviour of the fish, their environment, and the naturals. The clues to success are in those observations.

Remember that the majority of your fishing is matching your observation, and your wins will come from there. Very few opportunities are genuinely created when fishing — most are found by observing. If you notice trout sipping just below the surface but ignoring your dry fly, it's time to switch to an emerger or a soft hackle. If fish are picky in slack water, look for moving water. Sit and observe, pump a stomach, but be a detective looking for clues to solve the puzzle.

Technical example: when fishing an emergent pattern, try giving your line a slight twitch every few seconds. That makes your fly look like an emerging BWO trying to break through the surface.

Flies to carry

Because BWOs run small and you'll want to cover several stages, an assortment beats buying one pattern. The BWO Parachute and BWO Classic Dry cover the dun, with the Olive Comparadun and Baetis Cripple for the fish that refuse both. For the emerger and nymph stages that produce when they refuse your dry, the Barr's Baetis Emerger, the RS 2 Emerger and the Bead Head Pheasant Tail Assortment are the ones. And for the spinner fall, the Hi-Vis Rusty Biot Spinner solves the one real problem — seeing a spent wing at dusk.

Keeping a size 20 dry riding high is its own battle, so carry both a gel and a powder — Loon Aquel and Loon Dust. Browse all fly pattern assortments.

The bottom line

The allure of fly fishing lies in observation and its intricacies, and BWOs exemplify that. It might seem daunting at first, but with observation, patience, and practice you'll find success. Next time you're on the stream and the BWOs start to hatch, remember these tips.

Download the Dry Fly Tactics for Selective Trout eBook

Tight lines, everyone!

By Christian Bacasa
Host of the Fly Fishing Insider Podcast
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