BWOs are one of my favorite hatches. They hatch in good numbers, get fish rising, and require you bring your A-game for success. Here are a few tips to help you target the BWO hatch this Fall.

THE RIGHT WATER

BWOs don’t hatch everywhere on the river. They are “swimmer” mayflys and like slow to moderate speed runs-- Bonus points if it has some rooted aquatic vegetation. My favorite water is where riffles turn into runs/pools, like this spot on the SF Boise River.

HATCH WINDOW

The BWO hatch window typically is from 11am – 4pm. Hatches are water temperature and weather dependent: BWOs like to hatch on dark days. Overcast is good. Lite precip is even better. On sunny days you can still find them hatching some in the canyon shade. Like most bugs, BWOs have a preferred water temperature for hatching. In the Fall, they will start hatching when the water drops into the low 50s and continue hatching down into the low 40s. The SF Boise and Owyhee rivers both have BWO hatches later into the fall than the local freestone rivers because of warmer water from the tailwater dams.  Because of this, the hatch on the SF Boise goes well into December.

FISH THE FULL BUG LIFE-CYCLE

BWO hatches often occur in “waves”, and trout are most receptive to a fly during an “active hatch wave”.  In between hatch waves, take advantage of the time to adjust your position so you are ready to cast to a specific rise location. Part of the fun of a BWO hatch is figuring out what stage of the insect each fish is eating. BWO emergences  can be intermixed with spinner falls, and sometimes have 2 different sizes hatching-- making it difficult to identify what size or stage of the insect fish are keyed into. In general, I find that trout key in on emergers at the head of the run; on adult duns mid-run; and cripples or spinners in the tailout or eddies. BWOs spinnerfalls are often along the bank, so if you see a trout rising tight to the bank, serve him a spinner!

BWO FISHING TIPS

1. Come prepared to Match The Hatch – bring the full life-cycle of imitations. I like to fish a dun pattern with an emerger or spinner dropper.
2. Remember that not all trout are rising to the same life-cycle phase. Be prepared to switch flies when you target different fish (see the diagram above).
3. Bring your A-Game presentation. Avoid blind-casting. Station yourself to get the best drag-free drift and target specific fish.
4. Plan to fish a nymph 1-2 hours ahead of the hatch. Fish will move up to the head of the run to eat the nymphs.
5. On windy days, try a “knock-down” style pattern.
6. Take a minute to catch a bug sample and check the size and adjust your fly to match. Size matters on this hatch!

FLIES:

There are many good patterns out there--I think Dry Fly Innovations has some of the best. I particularly like their Colored Emerger and their Convertible pattern that you can make into a knock-down dun on the river. For nymphs you can't beat a Thread Frenchie or WD40. Check out Scott Blackhurst’s fly tying article for some more good patterns.