March Brown Mayfly: The Pacific Northwest's Premier Spring Hatch
Understanding the March Brown Mayfly Life Cycle
Despite its name, the March Brown (Rhithrogena morrisoni) doesn't always appear in March. In the Pacific Northwest, these remarkable insects emerge from mid-March through mid-April, with some hatches extending into May, depending on the river system and weather conditions.
Life Cycle Stages
1. Nymphal Stage
- Lives up to one year in the aquatic stage
- This means you can fish the nymphal stage year round, we like a larger hares ear
- Known as "clingers" due to their distinctive gill structure that acts like suction cups
- Inhabits fast, rocky runs and riffles
- Migrates to slower water as maturity approaches
2. Emergence Stage
- Typically begins in early afternoon
- Occurs in specific water conditions
- Nymphs swim to the surface to transform into duns
3. Adult Stage (Dun & Spinner)
- Duns emerge in early afternoon
- Spinner falls occur in late evening
- Adults live only 1-2 days, focused solely on mating
Prime Pacific Northwest Waters
Deschutes River
- Primary hatch period: Mid-March to mid-April
- Best sections: Middle Deschutes
- Look for moderate to fast riffles
Metolius River
- Not known for as consistent of a hatch, but you should be prepared with some in your fly box
- Clear water demands careful presentation
- Best during spring emergence
McKenzie River
- Excellent March Brown activity
- Focus on rocky runs and riffles
- Prime fishing during afternoon hatches
Optimal Fishing Conditions
Water Types
- Fast, rocky runs
- Well-oxygenated riffles
- Transition areas between fast and slow water
Weather Factors
- Hatches are more prolific following warmer winters
- Overcast days often produce better hatches
- Water temperature plays crucial role
Essential Fly Patterns
Nymph Patterns
- Traditional March Brown Nymph (sizes 10-12)
- Pheasant Tail Nymph
- Gold-Ribbed Hare's Ear
- Beaded Soft Hackle
Dun Patterns
- Parachute March Brown
- Comparadun Style
- Traditional Catskill Style
Spinner Patterns
- March Brown Spinner
- Rusty Spinner
- Spent-Wing Patterns
Fishing Techniques
Before the Hatch
- Focus on deep nymphing
- Target rocky runs
- Use weighted patterns
- Look for emerging rise patterns and fish a soft hackle
During the Hatch
- Watch for rising fish
- Switch to dun patterns
- Focus on seams and edges
Evening Spinner Falls
- Use spinner patterns
- Look for quiet water
- Pay attention to timing
Conservation and Habitat
Understanding the March Brown's habitat requirements helps anglers appreciate these insects' role in the ecosystem. They prefer clean, well-oxygenated water and are often indicators of healthy river systems.