March Brown Mayflies



The spring time revival of aquatic insects on Central Washington’s infamous wild trout stream, the Yakima River, triggers the emotions of fly anglers’ world wide as they seek out its waters each year.  “What time of year is best to fish the Yakima?”  This question is uttered to me time and time again by fly fishermen.  It can be a difficult question to answer because each month of the season is special in its own right.  My answer is usually based on the specific type of fishing each particular angler wants to accomplish or enjoys.  Nymph fishing with indicators, swinging streamer patterns or pounding the grassy banks with big attractors can fill in the gaps.  However, the majority of fly fishermen prefer the appeal of fishing dry flies to consistently feeding fish.  If this is the type of fishing you prefer, then the months of April and May are right up your alley.


As the month of March begins to wind down, hatches of Baetis (Blue Wing Olives) and Skawlla Stoneflies have been going steadily since the last days of February.  Dry fly fishing begins early on this desert river and most anglers never experience or overlook the importance of this first stonefly hatch.  Water conditions are generally low, given a normal winter and the Yakima rainbows have been foraging since the last hatches of November.  Exciting, big, bug fishing can quickly chase away the cabin fever that has set in over the long months of winter.


When the month of April arrives, warming temperatures and mild spring days will develop across the central basin.  With increasing water temperatures, the emergence of the Yakima’s most anticipated mayfly hatch of the season, the Rhithrogena Morrissoni or March Brown Mayfly, will begin to appear on the waters throughout the main stem of the Yakima.  This is the river’s most prolific, giant, mayfly emergence that will occur each afternoon during the months of late March, April and May.  Some years, the upper regions of the river will continually produce hatches of March Browns into the first parts of June.


As the early stages of this emergence begin to take place, larger more dominate trout will actively take naturals on the surface.  Most likely, Baetis Mayflies have been hatching for the past hour and attentions can quickly turn from the smaller dun to its larger counterpart, the March Brown.  As minutes quickly pass and the hatch intensifies, the larger of the trout will often disappear below the surface film and begin feeding on the struggling emergers.  Smaller, aggressive, trout will actively feed on the naturals stranded on the river’s surface.  During the peak of the emergence, this mayfly will be littered across the water.  A keen eye in combination with an imitation that floats drag free as well as passes the initial close up inspection of the trout will prove successful.  Trout generally won’t break their rhythm during this daily cycle of feeding.

Yakima River March Brown Nymph

The Yakima River March Brown

Yakima River March Brown

Yakima River March Brown Nymph

Yakima River March Brown Mayfly Dun

Yakima River March Brown Mayfly Dun

Excellent examples that imitate the natural mayfly in its adult dun stage are the Para-Wulff Adam’s, Para-Pheasant Tail or a standard March Brown pattern in sizes 12 and 14.  The white, upright wings of the Para-Wulff seem to present the appearance of a struggling insect and rainbows generally will commit without refusal to this pattern.  It also presents a highly visible silhouette for the angler.  If refusals do occur, a standard March Brown imitation can be used.


Most often times this is a high riding mayfly that uses it long arms to push its self atop the water.  It is slow to dry its colorful, mottled wing, so a standard pattern that duplicates the natural will at times be more productive.


The B.H. F.B. Pheasant Tail, Bubble Back Emerger or soft hackle P.T. are excellent patterns to replicate the sub-aquatic state of this insect.  Swinging soft hackle imitations under the first few inches of the surface film can provide anglers with some exciting, wet, fly fishing.  For those unwilling or find it difficult to present a drag free drift to feeding fish, the chances of action during the hatch are increased dramatically with a soft hackle swing.


Activity of the hatch can last anywhere from 20 minutes to an hour and a half.   Once a daily appearance of March Browns becomes consistent, an angler can set his watch to the time of their emergence.  On most days the hatch will begin sometime between 1:30 p.m and 2:00 p.m.  Positioning yourself on a section of river that is consistently producing a prolific emergence each day can provide an angler with some exciting match the hatch fishing.

For tying directions see our Fly Pattern Index!


Order Family Genus Species Body Color Wing Color Emergence

March Brown

EPHEMEROPTERA heptageniidie Rhithrogena Morrisoni Brown/Tan Brown Molted Afternoon

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