The Blue Winged Olive (BWO) Hatch in Oregon & Washington
Blue Winged Olives, also known commonly as BWOs and more scientifically as Baetis tricaudatus, are small mayflies that can be prevalent during the winter and spring months in our corner of the Pacific Northwest. They can be overshadowed by bigger bugs and more bountiful hatches the rest of the year, but during the winter and spring months, they really come to shine as there's very little else hatching. They are smaller bugs with olive bodies and dun/blue colored wings. While small in size, it makes up an important source of food for trout that have survived on nymphs.
While you can see BWOs throughout the year, depending on the weather, BWOs fish well during December to April, when other hatches are absent. The hatch really gains momentum starting in February as temperatures warm, and with consistent hatches taking place, trout are really looking up for this first hatch of the year. Look for them during the afternoons during the colder months and the mornings during the warmer months.
BWOs will hatch in the winter, typically at temperatures of 40 degrees or higher, but they prefer the warmer/more humid days with rain at any time of year. Look for them on the warmer days in winter, or the rainier days of the rest of the year. These bugs do not fare well during the dog days of summer or in high heat. Drier days can cause these mayflies' emergence difficulties and make their exoskeletons tougher to escape from.
What’s the best way to fish BWOs?
How to best fish BWOs largely depends on the conditions of the day and the fancy of the angler. They can be fished in a multitude of different water types. They are conducive to nymphing, swinging, dry fly, and emerger fishing in or just below the surface film. If you're seeing half-hearted rises or rolling rises, the fish are likely taking emergers. I often sit and watch for feeding fish, to see if they're taking duns off the surface or something just under the surface.
Small bugs call for small tippet. A 9ft leader tapered to 5X can do the trick, but this also depends on where you're fishing. If the water is slower, you may need to size down the tippet to 6X (and the fly), as fish will be more discerning. Typical sizes for BWO are 16-20. At times, you'll see 20 or 22, depending on your region and time of year.
Sometimes you’ll have to use a really small fly to get the fish's attention, and those smaller flies are hard to see. At times, this is because there are so many other natural bugs floating around, but also because people aren't casting as accurately as they could if they practiced! For a quick fix, drop a smaller BWO dry fly off the back of a larger, easier-to-see pattern. This will also help ensure you’re getting a good drift, even if you can’t see the smaller fly you’re actually fishing.
Recommended Blue Winged Olive Patterns
Your normal Hares Ear is a great nymph pattern. There are also a lot of BWO-flavored nymphs on the market these days – I'd recommend the Juju Baetis from Charley Craven or the WD-40 from Mark Engler.
For emergers and cripples, I like Bob Quigley's Quigley Cripple or Rene Harrop’s Last Chance. As for dries, I really like Jake’s Hatchback or Craig Mathews' Sparkle Dun for the dun pattern. When it comes to spinners, I'd recommend a Winna Spinna for its high-viz post. Or, you can use a classic like the Rusty Spinner. Another tremendous fly, although challenging to see as an angler, is the BWO Sprout. In a foam line, it can be hard to decipher if you are staring at your fly or foam.
With all of those near perfect imitations, don't be afraid to tie on a size 18 Purple Haze. To the trout, it must be the perfect silhouette, but for us, it offers a great pattern for visibility. With its high antron post tied into the hackle, it's a bit easier to spot in a feeding lane (foam is home).
Where to find a good Blue Winged Olive hatch
BWOs can be found throughout most of our watersheds in Oregon and southern Washington, but streams like the McKenzie River, Middle Fork Willamette River, Lower Deschutes River, and Crooked River offer some of the best opportunities around. Come get your BWO game dialed in with one of our phenomenal guides, or swing by the shop to talk technique.
Fishing BWOs, especially as dry flies or emergers, can be technical fishing. It’s the kind of fishing that makes you a better, more creative angler – and if you’re finding success, it probably means you’re leveling up your skill!
Life Cycle of the Blue Winged Olive
BWOs have a classic mayfly life cycle: egg, nymph, emerger, adult (dun), and spinner. Nymphs are agile swimmers, often active during low-light periods. When water temps warm just a bit, they’ll start emerging—drifting up to the surface, splitting their shucks, and becoming duns. After a brief stint as adults, they return as spinners to lay eggs, often in the evening.
About Joseph Beare
Joseph Beare is a guide for Northwest Fly Fishing Outfitters and a regular contributor to the NWFFO blog and newsletter. A former sports reporter, Joseph has been telling stories about outdoor and athletic endeavors for more than 20 years. As a guide, he specializes in unique trout trips, including local year-round water in winter, alpine expeditions on Mount Hood in summer and spring, and searun cutthroat floats in the fall. You can find him on Instagram @pdxflycollective.