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Friday, March 7, 2014

The March Brown Mayfly

March Brown

Scientific Names: Rhithrogena morrisoni, R. hageni

Common Names: March brown, western March brown

NYMPH SIZE: 8-12 mm (5/16 to 1/2 in)

NYMPH COLOR: Dark brown, sometimes olive-brown

DUN SIZE: 8-15 mm (5/16 to 5/8 in)

DUN COLOR: Wing: mottled brown and tan. Body: brown on top, tan below.

OTHER CHARACTERISTICS: Nymph: gills overlap under the abdomen; flattened appearance; three-tailed; head is wider than the abdomen. Dun has two tails.

March Brown Maddness

The spring time here in the Sierra Foothills and specifically on the Lower Yuba River is the time to get out on the lawn and start sharpening your dry fly strokes and presentations. It’s the time for the March Brown’s to make their presence felt. If you like the appeal of fishing dries to feeding fish, then the time of April and May is around the corner. March Browns are one of my most remembered and glorified hatches on the Lower Yuba River. Funny how that is, how as time goes on you forget the hours spent with refusal after refusal and remember the successes.

Even though the bugs often hatch in godawful weather and us fly fishers have spent many a March afternoon shivering, fishing a run as droplets of cold rain run down the sleeve of our casting arms, we would do it again tomorrow. We’d rather be there suffering and attempting to catch fish. As the month of March begins to wind down the hatches of Blue Wing Olives, "Baetis" and Skwala Stones, “Perlodidae," have been going on steadily since February a new player shows up. As late March and April arrives the days will typically start warming and the water temperatures will also go up which triggers the March Brown mayfly to start hatching. They can hatch in just about any weather. This is the "Rithrogenia Morrisoni" hatch. This large mayfly is typically an afternoon hatch and once it starts happening you can almost set your watch from it.

It seems though that for the past couple of years the March Brown hatch has not occurred with the intensity of past years on our Lower Yuba River. Whether this has to do with the changing structure of the river or from high water conditions channeling and rolling the river’s cobbled bottom I’m not sure. I am planning on observing this hatch closely this year will share the results. Any one else have any thoughts on this?

Where They Live

As members of the clinger group of mayflies (family Heptageniidae), March Brown nymphs live in riffles and fast, rocky runs. Nymphs are so well adapted to their habitat that they are seldom found in the drift until emergence time. As the nymphs near maturity, they migrate to slower (but not slow) water, usually within a hundred yards above or below a riffle.

Hatches usually start in the early afternoon. Just prior to the hatch, nymphs are often found drifting in the current, so it makes sense to present a nymph pattern near the bottom beginning a couple of hours before the hatch. As the nymphs hatch, they often drift a long distance before reaching the surface, so you find drifting nymphs anywhere from just below a riffle to runs that are well below them.

The Hatch

The March Brown hatch that takes place on the Lower Yuba River can be a complex hatch with BWO’s and PMD’s coming off and then the March Brown’s showing up to the dance, crashing the party.

On most days the BWO’s and PMD’s have been hatching for an hour or more and the trout’s attention can quickly turn to the larger March Brown’s. As trout switch their focus to the March Brown duns and you see surface rises, switch to a dry fly. This where having binoculars to scan the surface and see which bugs the fish are taking can really pay off. The March Brown duns usually emerge on the surface. As the early stages of the hatch begin to take place, larger and more dominate trout will actively take naturals on the surface.

Sometimes, however, emergence happens underwater as the dun floats to the surface. In this case a "flymph" or down-wing wet fly works best. As the hatch progresses the larger of the trout will often disappear below the surface film and begin feeding on the struggling emergers. Smaller more aggressive trout will still feed on top on naturals stranded in the film. During the peak of the emergence, March Brown’s can be littered across the water.

When fishing dries on the surface, being successful with the March Brown hatch requires an imitation that floats drag free and must pass a close inspection by the trout. Timing of the presentation is critical because the feeding trout won’t break their rhythm very often. 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. Swinging soft hackle imitations under the first few inches of the surface film can provide anglers with some exciting, wet fly fishing. 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, as mentioned earlier, you can set your 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.

I can't wait to retire my Switch rod, shot, indicators and such for a while and break out my 5 weight.


March Brown research from and Rick Hafele at

Photos of March Brown's also from

1 comment:

Have any Questions or Comments? Let me know, Clay.