THE GREAT OUTDOORS — For most fly fishers, the blue-winged olive mayfly hatch, the time when the aquatic insect larvae begins to hatch, signals the beginning of the dry fly fishing season and is a great time to grab your rod and head outdoors.

Blue-winged olive mayflies, also known by their scientific name, baetis, are most commonly called BWO's by many fly fishers.

What is the blue-winged olive mayfly hatch and why is it a good time for fishing?

A "hatch" is the simplified explanation for the emergence period for when immature aquatic insects that live on the river bottom begin to mature and change into adults. For blue-winged olive mayflies, this emergence happens when the nymph leaves the river bottom and swims to the river surface. At the surface, the winged adult, known as a dun, will climb out of its shell and ride on the surface current as its wings dry. This is a very vulnerable time for the insect and trout rise up and feed on them.

While floating on the river surface, blue-winged olive mayflies will test their wings periodically. This fluttering of their wings will produce several incomplete liftoffs. Oftentimes, the fluttering will cause the mayfly to spin and skitter upstream a bit. Some trout will key in on this motion and it is not uncommon to see trout close to the surface chasing down the fluttering bugs. Most of the time, it is the smaller trout doing the chasing, but sometimes, wise old larger trout will also give chase, especially if they are fished over a lot.

Trout also often find a good feeding lane by locating large groups of the insects and waiting for the current to bring the helpless floating bugs to them. Small trout make showy, splashy rises to the surface while larger trout simply poke their head through the surface film and gently eat the mayflies without much disturbance.

When does the hatch occur and when are good times to go fishing?

In spring, the blue-winged olive mayfly hatch typically occurs during March and April. The prime emergence time for the insects is during the warmest part of the day between 10 a.m. and 2 p.m. Some of the best blue-winged olive mayfly hatches occur on overcast days, but don't overlook blue-sky days as the hatches will still be found in good enough numbers to get trout feeding.

Good blue-winged olive mayfly fly patterns

Fly tiers are constantly trying to come up with the "new" and "improved" fly pattern for blue-winged olive mayflies. A quick internet search will provide pictures, video and instruction to tie several good patterns.

Two of the best patterns used to imitate the natural insect is the comparadun pattern and the standard Adam's pattern. The natural insects tend to have bodies with hints of gray, brown and olive-green with wings gray with a hint of pale blue. An Adam's dry fly pattern. Tying the fly parachute style with a little olive added to the gray body is a very effective pattern. Blue-winged olive mayfly patterns are tied on size 16-20 hooks.

Several patterns are available for fishing a Blue-winged olive mayfly nymph. Some of the more popular blue-winged olive mayfly patterns are hare's ear, pheasant tail, RS2, WD40 and barr's emerger.

Basic fly fishing techniques

Before the adult blue-winged olive mayfly duns are seen floating on the surface, fly fishers can use nymph patterns below the surface. A simple setup with the fly at the end of the tippet, a small split-shot about 12-18 inches up the leader, and a small indicator (fly fisher's small bobber) on the leader about two times the water depth usually results in successful fishing. Having an indicator that can easily adjust works best. This allows the rig to be adjusted for different water depths.

As the nymphs begin to emerge and trout begin to eat them as they rise through the water column, an emerger pattern floating just below the water surface will bring good results.

Another great technique is to use soft-hackled wet flies. Cast these patterns down and across stream and swing them in front of active fish.

When the blue-winged olive mayfly duns are on the surface and fish are taking them, dry fly fishers will switch to a floating imitation. This is when fly fishers need the ability to present an imitation in a "drag free drift." A drag free drift is nothing more than the ability to cast a fly pattern upstream and have it float the same speed as the current.

Drag happens when the fly line is pulled by the current, making the fly pattern move faster than the current. That often creates a V-wake in the surface behind the fly pattern. Because a V-wake and fly moving faster than the current is unnatural, very few trout will hit a dragging fly pattern.

Trout watching for the non-angler

For those who love the outdoors and love to be around rivers but don't fish, learning to watch feeding trout is quite enjoyable. Find a nice section of water and watch the surface for floating bugs and feeding fish. If you are quiet and sneaky, you can watch for the telltale ripples on the water's surface, indicating a trout has surfaced. Once you see the rise ripples, try to position yourself closer to the water. Stay below the trout, as often, they are facing upstream. Look into the water and see if you can spot the trout. Then watch it rise and sip the mayflies as they come downstream.

A good pair of polarized sunglasses will help take the glare off the water. Notice how the blue-winged olive mayflies behave as they float and flutter, and watch as some of them get airborne and rise into the sky. Try to locate the biggest trout and smile at the splashy eagerness of the smaller ones.

Whether you love to fly fish or love to explore and learn about the river environment, witnessing the blue-winged olive mayfly emergence can add to your spring-time enjoyment of the outdoors.

Robert Williamson is a graduate of Weber State College and the author of "Creative Flies: Innovative Tying Techniques."

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