Blue-winged olive
Also called BWO, Baetis, Blue wing olive, Blue-wing olive
“Blue-winged olive” (BWO) is the common fly-fishing name for several small mayflies in the Baetis group. Anglers use it to describe the hatch and the flies used to match it.
- Group
- Mayfly hatches
- Category
- Entomology & forage
- Level
- Beginner
- Water
- Freshwater
Last updated
What Blue-winged olive means
In fly fishing, “blue-winged olive” usually means a Baetis-type mayfly hatch and the bugs involved—nymphs, emergers, duns, and spinners. The adults typically show olive to brownish bodies with gray-blue wings, but color and size vary by river and species.
BWOs are known for hatching in cool, unsettled weather. On many trout waters that means spring and fall, and on some tailwaters it can happen through winter. When people say “BWO day,” they’re often talking about steady, smaller mayflies coming off for a while rather than a short, explosive hatch.
Common ways to fish a BWO situation include a small mayfly nymph under an indicator, a dry-dropper with a BWO-style nymph below, or a dry or emerger when fish start feeding in the film. If spinners show up later, a low-riding spinner pattern can matter more than a high-floating dry.
Why it matters on the water
“BWO” is a clue about timing and fish behavior. These hatches often bring trout up in softer seams and edges to pick off emergers and duns, and the takes can be quiet and easy to miss. Knowing that keeps the focus on drag-free drifts, finer tippet, and patterns that sit in or just under the surface.
It also helps with fly choice when the water looks “buggy” but nothing obvious is happening. In a lot of BWO windows, fish eat nymphs and emergers before they commit to adults. Starting subsurface and moving up the column as rises become consistent saves time.
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Read next
- ComparadunA Comparadun is a mayfly imitation tied without hackle, using a flared deer-hair wing and a tapered body to sit low and look like a dun.
- Pheasant Tail NymphA slim, buggy nymph pattern tied with pheasant tail fibers, usually to imitate mayfly nymphs. It’s a standard “search” nymph for trout and other freshwater fish.
- SpinnerA spinner is a dry fly that imitates an adult mayfly after it has mated and fallen spent on the water, usually with wings laid flat to the sides.
- TricoTrico is a tiny mayfly (genus Tricorythodes) best known for dense summer morning hatches and spinner falls. On many trout rivers it brings selective fish and fine-tippet dry-fly fishing.
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