The Blue-Winged Olive Hatch

By Scott Richmond

Deschutes River, late February. From the bottom of the canyon, gray is the only color visible beyond the rimrock. From that leaden ceiling, raindrops fall for awhile then stop, uncertainly.

However, the picture is much more pleasant at my feet than over my head: trout make silver streaks, like flashbulbs going off, as they feed on emerging mayflies. Many aggressive, wild redsides, averaging 14-16 inches, are active in the backeddy. Each is bright pink; it's not their year to spawn.

A few more raindrops fall, and a windgust makes me turn up my collar. Something other than the wind gives me a shudder, though. Did I turn off the car's lights? Should I run a mile back down the road and check? More flashes in the river; they're taking blue-winged olives in a major hatch. I have the right flies, I know what to do, I have the river to myself. When's the next time it will come together like this?

When I reached the car a couple of hours later, every single electron had drained out of the battery, and it took several hours and a three-mile walk to get it going again. But it was worth it to catch over a dozen redsides on a dry fly on a winter day. Batteries are easier to recharge than souls.

From September through April, blue-winged olives (BWOs) hatch on western rivers, but the hatches are strongest mid-February through early April. More than one angler has told me that the best dry fishing he ever had on the Deschutes was in February--during the a BWO hatch. On the other hand, it's an unreliable and unpredictable hatch. When it's good, it's very good. And when it's bad . . . well, it's still nice to get out and be on the river. Below, you will find basic BWO biology, flies and tactics, and a few special hints to help you get the most out of the hatch.

Biology

Blue-winged olives are mayflies from the family Baetidae. Entomologists can have endless debates over the number of distinct genera and species within this family, but those discussions are of little value to anglers. The general appearance, habitat, and life cycle of these insects are quite similar, and that's what matters to fish and fishermen. Any western aquatic insect listed as a Baetis (properly pronounced Bee-tiss, not Bait-us), Pseudocloeon, or Diphetor qualifies as a blue-winged olive, or BWO.

BWOs are "swimmer" mayflies, meaning they are slender and flip their tails to propel themselves. Most species live where the water flows at a slow to moderate pace. They inhabit the small spaces between river rocks, and graze on diatoms and algae. One species prefers the kind of riffly water you associate with stoneflies (see a previous article). BWO nymphs have a habit of drifting in the current, especially near sunrise and sunset; we presume they are searching for a new lunch counter.

At maturity, nymphs buoy to the surface, the skin splits, and the winged dun crawls out. After a brief rest on the river's surface, the dun flies off, molts into the spinner stage, and mates. Females return to the water to lay eggs. Some females lay eggs by crawling underwater down logs and rocks.

BWOs vary in color and size, but most duns are small (matched by size 18-22 dry flies) and have smoky-blue wings. Body colors range from gray-olive to brown. Nymphs are dark brown.

Throughout the West, BWOs are abundant enough to be interesting to trout and cause selective feeding. In the winter, they are a staple of the trout diet. That makes them vital to fly anglers.

Flies and Tactics

Trout will be most receptive to BWOs when large numbers of insects are present and are most vulnerable. This means:

  1. Nymphs drifting near the bottom nearly any day from September through April. A Pheasant Tail is a good imitation, but the traditional Gold-Ribbed Hares Ear is particularly effective in September because the BWOs present at that time have two light-colored abdominal segments that are well-imitated by the fly's gold ribbing. In September, dead-drift the fly in the water just downstream from a riffle (where the river deepens and slows). The rest of the year, concentrate your nymphing in water with a slow to moderate flow.
  2. Emerging duns. Because BWOs are small, the surface of smooth water is a barrier to them, and many are trapped just below the surface or must struggle to break through the water's surface tension. At this point they are highly vulnerable to trout, and they are frequently taken just subsurface. Several patterns work as emergers: try the Baetis Cripple or CDC Cripple . Olive or brown-olive bodies work best. The best places are moderate to slow runs and backeddies. The presentation is the same as if you were fishing a dry fly. John Smeraglio, owner of the Deschutes Canyon Fly Shop in Maupin, has an effective strategy. He casts a Soft Hackle upstream, then lifts the rod as the fly drifts back towards him ("high sticking"), then lowers the rod as the fly passes. At the end of the dead drift, he lets the fly swing across in the current. Strikes can come either on the drift or on the swing.
  3. Drying Dun. As the dun dries its wings, it is helpless to escape. A dry fly work can work quite well in backeddies and slow runs. Good patterns include the Sparkle Dun , CDC Comparadun , or Parachute Baetis .
  4. Egg-laying Female. BWO spinner falls are seldom important on western waters, but females that crawl below the surface to lay eggs are often knocked loose and are taken by trout. A Soft Hackle works well here. Put a small shot on the leader and cast upstream, giving the fly time to reach the bottom. Then jig the rod to give the fly some action.

Additional Tips

  1. Fish the backeddies. During a hatch, backeddies are usually more productive than runs. The duns get trapped and seem to circle endlessly--or until a trout sucks them down. For a trout, the backeddy is a quiet, safe place where meals are presented on an endless "lazy susan."
  2. Learn to make slack casts. To overcome the intricacies of a backeddy's currents, learn to make pile casts and wiggle casts. These slack line casts will give you a few precious moments of drag-free drift.
  3. Don't ignore subsurface opportunities. Too many fly anglers ignore the subsurface action offered by emergers and egg-laying females.
  4. Cast to foam lines and current pushes. When fishing backeddies, watch the lines of foam. The current that concentrates foam also concentrates insects and the trout that eat them. Cast so your fly lands in the foam line. Sometimes the current surges and creates a "push" of foam. When this happens, cast to its leading edge; that's where the trout are.
  5. Sometimes you need a finer leader. On streams such as the Metolius and Fall rivers, you often need to go to a 7X tippet because of the clear water and fussy trout. On the Deschutes, however, a 5X tippet is usually adequate, but sometimes you need the flexibility of a 6X tippet so the fly will wiggle more naturally in the current.
  6. Separate yourself from the crowd. One winter day on the Deschutes, I encountered one of the most massive BWO hatches I'd ever witnessed. I cast my Sparkle Dun into the backeddy, where it joined thousands of natural insects. A trout would rise, I would strike . . . then curse as I realized the trout had taken a dun two feet from my fly. My imitation was excellent--too excellent, since I couldn't distinguish it from the multitude of real insects. I solved the problem by tying on a slightly darker version of the same pattern. Now I could spot my fly in the crowd. The trout didn't care that it wasn't an exact match, and I had outstanding fishing.
  7. Nothing is certain. I've never spent a winter day on a Western stream when there weren't a few BWOs hatching in the early afternoon. Never. But the strength of the hatch is notoriously variable, and it often fails to gather enough energy to interest trout. The best days are overcast and drizzly, the worst are warm and sunny. But some sunny days have produced outstanding hatches; conversely, I've sat shivering in a cold rain expecting a major BWO hatch, then saw only a handful of duns and one small, half-hearted trout that rose--once. If you go to the river you might have a decent hatch and good fishing, but if you stay home you are certain to catch nothing.

Scott Richmond is Westfly's creator and Executive Director. He is the author of eight books on Oregon fly fishing, including Fishing Oregon's Deschutes River (second edition).