July is the month, late evenings are the time, and yellow mayflies are the
main course.

Local lakes will soon be the incubator for the yellow mayfly (Hexagenia
limbata) hatch. This 1 1/4-inch insect is the most geographically widespread
mayfly species in North America — and the Mountain environment is included.

Locally, the best known Hex hatches occur from Lost Lake, Timothy Lake, the
private lakes on Rocky Ridge Ranch and Merrill Lake in southern Washington.

When fishing during a Hex hatch, there is no need to get to the water before
late afternoon. This is the perfect situation for the angler who wants to do
some fishing after the day’s work is done.

A brief history of the mayfly life cycle tells us why.

The female Hex deposits her eggs directly on or in the water. Individual
females release as many as 8,000 oval eggs, each less than one-half mm in
length, which immediately sink to the lake bottom.

After several days to several months (depending on water temperature), a
tiny nymph hatches from the egg. It immediately burrows into the lake
sediment to feed on particulates and to construct a U-shaped burrow with two
opening at the sediment surface.

The nymph continually enlarges its burrow as it grows so that the burrows of
mature nymphs can be as much as five inches deep. By undulating its body
and moving its feathery abdominal gills in sweeping motions, the nymph
keeps the burrow oxygenated.

The nymph life lasts from about one year in warm climates to two years in
colder regions – which is the case in Pacific Northwest lakes.

As with all insects, they grow by shedding their exoskeleton in a process
called molting. When the nymph is ready for its final molt, it leaves the
burrow at dusk or soon after and rapidly swims to the lake surface, where its
exoskeleton splits lengthwise down its back.

From the raft-like exoskeleton emerges a fully winged subimago, or dun,
which after only a few minutes takes flight.

This winged Hex is the only stage in the insect’s life cycle that most people
see.

This is where the crafty angler comes into play.

You will usually see a few duns around 7 p.m. This is a false hatch. Unless
there is dense cloud cover the real hatch starts between 8:30 p.m. and 9 p.m.
The best anglers will work from a boat or float tube. Very few places have
been encountered where fishing can be done from shore or while wading. If
you are in a boat be very quiet as the trout are easily spooked and will quit
feeding on a hint of noise.

The angler should start fishing over Hex beds with a sinking line and a Hex
nymph fly. The sink rate of the line you choose is dependent on the depth of
the water. Let the fly sink to within a foot of the bottom and retrieve it fairly
rapidly. A stout leader is advisable.

As the hatch progresses both the fish and the nymphs will start to concentrate
near the surface. Consequently, you should carry two rods, one with a floating
line and the other with a sinking line.

When there is sufficient surface action switch to the nymph on the floating line
and retrieve it slowly just under the surface of the water.

Recently we have been experimenting with a floating nymph. Many fish focus
on the nymph just as it starts to hatch in the surface film. During this process,
the nymph is helpless. It can neither swim nor fly. The floating nymph has
proven to be a deadly fish catcher.

As darkness falls and duns start to appear in sufficient number that fish start
to concentrate on them, switch to a dry fly pattern. During this part of the
evening a peaceful calm usually descends on the lake and the huge flies are
only pale apparitions on the inky surface. In the failing light it becomes hard
to tell your fly from the real thing.

So you strike at any rise that is in the vicinity of where you think your fly is,
and are sometimes rewarded with a bent rod and the pulse of a heavy fish.

And this is why we fish.