Midge
Chironomidae spp.
Midge
- Peak week
- Year-round
- Intensity
- Heavy
- 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
Primary winter food
Hatch calendar
Gunpowder Falls hatch calendar.
- Tailwater
- Catch and release / wild brown trout
- brown trout
- wild
Cold tailwater within an hour of Baltimore and DC — wild brown trout fishery with reliable Sulphur hatches and a long catch-and-release section.
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.
Blue Winged Olive
Baetis spp.
Mayfly- Peak week
- Mar 25 – Apr 25
- Intensity
- Heavy
- 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
Sulphur
Ephemerella dorothea / invaria
Mayfly- Peak week
- May 25 – Jul 5
- 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
Pale Morning Dun
Ephemerella excrucians
Mayfly- Peak week
- Jun 15 – Jul 25
- Intensity
- Heavy
- Time of day
- Morning
- Water temp
- 55–68°F · peak 60°F
Top flies
PMD Parachute #16-18 · PMD Comparadun #16 · Rusty Spinner #16-18
Morning emergence
Tan Caddis
Hydropsyche spp.
Caddis- Peak week
- Jun 1 – Sep 15
- Intensity
- Heavy
- Time of day
- Evening
- Water temp
- 58–72°F · peak 64°F
Top flies
Elk Hair Caddis #14-16 · X-Caddis #14 · LaFontaine Sparkle Pupa #14
Hendrickson
Ephemerella subvaria
Mayfly- Peak week
- Apr 20 – May 15
- Intensity
- Moderate
- 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
Full year calendar
Twelve months on Gunpowder Falls.
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 Gunpowder Falls
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.
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.
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.
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.
Pale Morning Dun
Ephemerella excrucians
MayflyMorningWater-temperature trigger
30°F55–68°Fpeak 60°F80°F- Duration
- 6 weeks
- Also called
- PMD
Top fly patterns
- PMD Parachute #16-18
- PMD Comparadun #16
- Rusty Spinner #16-18
- Pheasant Tail #16
More reliable on tailwaters where stable temps suit the hatch. Often runs concurrently with Sulphurs but emerges in morning rather than evening.
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.
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.
Trico
Tricorythodes spp.
MayflyMorningWater-temperature trigger
30°F60–75°Fpeak 68°F80°F- Duration
- 8 weeks
- Also called
- White-Winged Black · Curse
Top fly patterns
- Trico Spinner #20-24
- Trico Parachute #22
- CDC Trico #22
Tiny black-bodied mayfly. The spinner fall — not the dun emergence — is the main event. Look for clouds of spinners over flat water at sunrise.
River info
- River type
- Tailwater
- Primary species
- brown_trout · wild
- Management
- Catch and release / wild brown trout
- Counties
- Baltimore County
- Elevation
- 350 ft
- Access
- Gunpowder Falls State Park — substantial public access from Prettyboy Reservoir downstream.
Live water temperature & hatch alerts.
Bield Fish reads USGS gauges, watches for the trigger window, and pings you when Gunpowder Falls hits the temperature for your target hatch.
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