Hendrickson
Ephemerella subvaria
Mayfly
- Peak week
- Apr 25 – May 15
- Intensity
- Heavy
- Time of day
- Afternoon
- Water temp
- 50–58°F · peak 55°F
Top flies
Hendrickson Parachute #12-14 · Red Quill Spinner #12-14 · Pheasant Tail Nymph #14
Hatch calendar
Big Gunpowder Falls (freestone upper) hatch calendar.
- Freestone
- Stocked
- brown trout
- rainbow trout
- stocked
Upper freestone reaches of the Gunpowder before it enters the reservoir system — smaller-water wading and a short shoulder season.
Verify with the agency before fishing
Fishing regulations change every season. This page is a summary maintained by Bield — bag limits, exact dates, and species-specific rules must be verified with Backwater Angler before each trip.
What's hatching now
May on the water.
Sulphur
Ephemerella dorothea / invaria
Mayfly- Peak week
- May 25 – Jun 25
- Intensity
- Heavy
- Time of day
- Evening
- Water temp
- 55–68°F · peak 62°F
Top flies
Sulphur Parachute #16-18 · Sulphur Comparadun #16-18 · Sulphur Sparkle Dun #16
Midge
Chironomidae spp.
Midge- Peak week
- Year-round
- Intensity
- Moderate
- Time of day
- Midday
- Water temp
- 32–60°F · peak 40°F
Top flies
Griffith's Gnat #20-24 · Zebra Midge #20-22 · WD-40 #20
Blue Winged Olive
Baetis spp.
Mayfly- Peak week
- Apr 1 – Apr 25
- Intensity
- Moderate
- Time of day
- Afternoon
- Water temp
- 45–55°F · peak 50°F
Top flies
Parachute BWO #18-20 · CDC Comparadun #18-20 · Pheasant Tail Nymph #18
Spring emergence
Quill Gordon
Epeorus pleuralis
Mayfly- Peak week
- Apr 15 – May 5
- Intensity
- Moderate
- Time of day
- Afternoon
- Water temp
- 48–56°F · peak 52°F
Top flies
Quill Gordon Dry #12-14 · Quill Gordon Wet #12 · Pheasant Tail Nymph #14
Grannom Caddis
Brachycentrus spp.
Caddis- Peak week
- Apr 25 – May 15
- Intensity
- Moderate
- Time of day
- Afternoon
- Water temp
- 52–62°F · peak 56°F
Top flies
Elk Hair Caddis #14-16 · Henryville Special #14-16 · LaFontaine Sparkle Pupa #14
March Brown
Maccaffertium vicarium
Mayfly- Peak week
- May 10 – Jun 5
- Intensity
- Moderate
- Time of day
- Afternoon
- Water temp
- 55–65°F · peak 60°F
Top flies
March Brown Parachute #10-12 · Grey Fox Comparadun #12 · March Brown Nymph #12
Light Cahill
Stenacron / Leucrocuta spp.
Mayfly- Peak week
- Jun 5 – Jul 5
- Intensity
- Moderate
- Time of day
- Evening
- Water temp
- 60–72°F · peak 65°F
Top flies
Light Cahill Parachute #14-16 · Cahill Comparadun #14 · Light Cahill Spinner #14
Full year calendar
Twelve months on Big Gunpowder Falls (freestone upper).
Each row is a hatch species. Bar color = type, opacity = intensity, peak month outlined. The current month is highlighted on the timeline.
MayflyCaddisStoneflyMidgeTerrestrial· peak month outlined · intensity = bar opacity · current month highlighted
Hatch species on Big Gunpowder Falls (freestone upper)
The bug calendar in detail.
Midge
Chironomidae spp.
MidgeMiddayWater-temperature trigger
30°F32–60°Fpeak 40°F80°F- Duration
- 52 weeks
- Also called
- Chironomids · Snowflies
Top fly patterns
- Griffith's Gnat #20-24
- Zebra Midge #20-22
- WD-40 #20
- Disco Midge #22
Year-round food source — the only consistent option on tailwaters in winter. On cold sunny days look for noses sipping clusters in slow water.
Early Black Stonefly
Capnia / Allocapnia
StoneflyMiddayWater-temperature trigger
30°F38–50°Fpeak 42°F80°F- Duration
- 4 weeks
- Also called
- Little Black Stonefly · Winter Stonefly
Top fly patterns
- Black Stonefly #16-18
- Black Beadhead Nymph #16
- Small Black Stimulator #16
Cold-water freestone stonefly, often seen crawling on snow banks. Trout key on the nymphs more than adults.
Blue Winged Olive
Baetis spp.
MayflyAfternoonWater-temperature trigger
30°F45–55°Fpeak 50°F80°F- Duration
- 6 weeks
- Also called
- BWO · Olive
Top fly patterns
- Parachute BWO #18-20
- CDC Comparadun #18-20
- Pheasant Tail Nymph #18
- RS2 #20
Most reliable Eastern hatch. Two emergences — spring (March-April) and fall (September-October). Best on overcast, drizzly days.
Quill Gordon
Epeorus pleuralis
MayflyAfternoonWater-temperature trigger
30°F48–56°Fpeak 52°F80°F- Duration
- 3 weeks
- Also called
- QG
Top fly patterns
- Quill Gordon Dry #12-14
- Quill Gordon Wet #12
- Pheasant Tail Nymph #14
Classic Catskill spring hatch. First major mayfly of the year on many freestone streams. Emerges underwater — wet flies often outperform dries.
Hendrickson
Ephemerella subvaria
MayflyAfternoonWater-temperature trigger
30°F50–58°Fpeak 55°F80°F- Duration
- 3 weeks
- Also called
- Red Quill · Dark Hendrickson
Top fly patterns
- Hendrickson Parachute #12-14
- Red Quill Spinner #12-14
- Pheasant Tail Nymph #14
- Hendrickson Comparadun #14
First substantial mayfly hatch on most Eastern rivers. Spinner falls in evening can be as productive as the dun emergence.
Grannom Caddis
Brachycentrus spp.
CaddisAfternoonWater-temperature trigger
30°F52–62°Fpeak 56°F80°F- Duration
- 3 weeks
- Also called
- Apple Caddis · Mother's Day Caddis (East)
Top fly patterns
- Elk Hair Caddis #14-16
- Henryville Special #14-16
- LaFontaine Sparkle Pupa #14
- Green-bodied Caddis Nymph #14
First major caddis emergence of the year. Look for clouds of small dark caddis above riffles in late afternoon.
March Brown
Maccaffertium vicarium
MayflyAfternoonWater-temperature trigger
30°F55–65°Fpeak 60°F80°F- Duration
- 4 weeks
- Also called
- Grey Fox · American March Brown
Top fly patterns
- March Brown Parachute #10-12
- Grey Fox Comparadun #12
- March Brown Nymph #12
Sporadic emergence rather than a heavy hatch — but trout key on individual large duns drifting through. Freestone-river specialty.
Sulphur
Ephemerella dorothea / invaria
MayflyEveningWater-temperature trigger
30°F55–68°Fpeak 62°F80°F- Duration
- 6 weeks
- Also called
- Pale Watery · Little Yellow May
Top fly patterns
- Sulphur Parachute #16-18
- Sulphur Comparadun #16-18
- Sulphur Sparkle Dun #16
- Pheasant Tail Nymph #16
- Sulphur Spinner #18
The most important mayfly hatch on Eastern rivers. Reliable emergence + spinner fall every evening for 4-6 weeks. Match the spinners with rusty-bodied patterns.
Light Cahill
Stenacron / Leucrocuta spp.
MayflyEveningWater-temperature trigger
30°F60–72°Fpeak 65°F80°F- Duration
- 5 weeks
- Also called
- Cahill
Top fly patterns
- Light Cahill Parachute #14-16
- Cahill Comparadun #14
- Light Cahill Spinner #14
Pale yellow-cream mayfly. Less intense hatch than Sulphur but reliable across many Eastern rivers in late spring through early summer.
Yellow Sally Stonefly
Isoperla spp.
StoneflyAfternoonWater-temperature trigger
30°F58–70°Fpeak 64°F80°F- Duration
- 5 weeks
- Also called
- Little Yellow Stone
Top fly patterns
- Yellow Sally Stimulator #14-16
- Yellow Stonefly Nymph #14
- Yellow Elk Hair Caddis #14
Common on freestone rivers. Adults flutter back to lay eggs on warm afternoons — trout target the egg-laying females.
Tan Caddis
Hydropsyche spp.
CaddisEveningWater-temperature trigger
30°F58–72°Fpeak 64°F80°F- Duration
- 10 weeks
- Also called
- Spotted Sedge · Cinnamon Caddis
Top fly patterns
- Elk Hair Caddis #14-16
- X-Caddis #14
- LaFontaine Sparkle Pupa #14
- Tan Caddis Soft Hackle #14
Workhorse summer caddis. Heavy emergences and egg-laying flights at dusk through summer. Drop a soft hackle on the swing during the evening.
Slate Drake
Isonychia bicolor
MayflyEveningWater-temperature trigger
30°F55–70°Fpeak 62°F80°F- Duration
- 12 weeks
- Also called
- Iso · Mahogany Dun (spinner)
Top fly patterns
- Slate Drake Parachute #12
- Iso Comparadun #12
- Mahogany Spinner #12
- Iso Nymph #12 (swimming nymph)
Long-running hatch from June into October. Nymphs are strong swimmers and crawl out of the water to emerge — fish a swung wet fly through riffles.
Terrestrials
(beetles, ants, hoppers)
TerrestrialAfternoonWater-temperature trigger
30°F60–78°Fpeak 70°F80°F- Duration
- 12 weeks
- Also called
- Hoppers · Ants
Top fly patterns
- Foam Hopper #10-12
- Foam Beetle #14-16
- Para-Ant #16-18
- Chernobyl Ant #10
Not a hatch but the most important summer trout food in many Eastern systems. Fish tight to grassy banks and overhanging trees. Hopper-dropper rigs are deadly July through September.
October Caddis
Pycnopsyche spp.
CaddisEveningWater-temperature trigger
30°F50–62°Fpeak 56°F80°F- Duration
- 4 weeks
- Also called
- Fall Caddis · Great Brown Sedge
Top fly patterns
- Orange Stimulator #10-12
- Goddard Caddis #10
- October Caddis Pupa #10
- Orange Elk Hair Caddis #10
Large orange-bodied caddis. The big fall food source on cold freestone rivers. Trout eat them all day in October but the egg-laying flight at dusk is the most explosive feeding.
River info
- River type
- Freestone
- Primary species
- brown_trout · rainbow_trout · stocked
- Management
- Stocked
- Counties
- Baltimore County
- Elevation
- 450 ft
- Access
- Public access in Gunpowder Falls State Park; smaller water than the lower tailwater.
Live water temperature & hatch alerts.
Bield Fish reads USGS gauges, watches for the trigger window, and pings you when Big Gunpowder Falls (freestone upper) hits the temperature for your target hatch.
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