Tailwater · Mixed Metamorphic · Maryland, US

Gunpowder Falls

A rocky pool on the Gunpowder Falls river surrounded by autumn foliage, with a large boulder in the foreground.

The Gunpowder below Prettyboy Dam is a small miracle — a seven-mile tailwater of wild brown trout half an hour north of downtown Baltimore.

Today · Not the day for it
Pheasant Tail Nymph (18-20)
Forecast · Today
Not the day for it
Not much stacked in your favour today. Worth an hour if you are nearby, not worth the special trip.
45% projected
Today's fly
Pheasant Tail Nymph (18-20)
Pheasant Tail Nymph (18-20)
Conditions on the water · Today
Live gauge
Level
Rising
0.39 m
Lifting fast
Water temp11.5°C
ClarityUnfishable
Weather27°C
WindN 9 km/h
Pressure1018 hPa
Rain · recent0.5 mm
Rain · ahead0.7 mm

The nearest gauge doesn't record temperatures, so we've estimated it — defer to the river keeper's advice.

Water temperature for Brown Trout
Ideal
12°C est.ideal 10–16°C
0°14°28°
How to fish it · for Brown Trout
When
Nymphing can work through most of the day.
Where
Cover mixed depths.
Method
Start with tight-line nymphs and adjust if fish rise or drift higher.
Kit
9 ft #4 rod, floating line, 12 ft tapered leader to 4–5 lb fluoro tippet.
Why this works
Excellent — water temperature is right today, though insect activity could be better.
Likely species
Mayflies
Caddisflies
terrestrials
Hatch timeline · todayPeak at 12pm

12pm(now) — Eastern Blue-Winged Olive

Stage: On emergersApproach: Emerger or dryActivity: 59%
Also:Black Midge29%
Peak emergence windowWeather boost5 food groups active

Peak activity at 12pm — Eastern Blue-Winged Olive (Eastern Blue-Winged Olive, Peak emergence window)

Sub-surface · on the nymphunder the surface

Hatch predictions

Top nymph shown — see all 4 guilds with Pro.

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Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

Top prey shown — see all 5 with Pro.

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Evidence
Records-basedModerate confidence

Based on species-occurrence records, not local invertebrate surveys.

Through the year
0–3 scale · September highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
2
2
2
2
2
1
SulphurHatch
2
3
2
Trico (Eastern)Hatch
2
3
3
2
Eastern Blue-Winged OliveHatch
2
3
3
3
3
3
3
3
2
Eastern Summer BWO (Drunella)Hatch
2
3
3
2

Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.

Ranked for today
Brown Trout fly box
Permits & access
Permit required — see local rules.
  • Maryland licence required; catch-and-release wild trout regulations on the tailwater reach — verify current MDNR rules and the fly-fishing-only sections.
What's coming
Plan ahead
5-day outlook
Gallery · 2
  1. A rocky pool on the Gunpowder Falls river surrounded by autumn foliage, with a large boulder in the foreground.
    Autumn Along the Gunpowder
  2. Terrain map of the venue
    Terrain map
About this water

The Gunpowder below Prettyboy Dam is a small miracle — a seven-mile tailwater of wild brown trout half an hour north of downtown Baltimore. Back in the eighties, Maryland's DNR and Trout Unlimited talked the dam operators into a guaranteed minimum cold release, and the browns took it from there; the river hasn't been stocked since, and it doesn't need to be. It's tight, technical, tree-lined water — sulphurs and caddis in season, midges and scuds the rest of the year, and trout that have seen every fly in the box. Read the release out of Prettyboy and fish small.

  • Mixed metamorphic
Water quality · US Clean Water Act
  • Aquatic life: Not assessed
What this classification means

EPA ATTAINS assessment unit 'Gunpowder Falls' (MD-02130805-Gunpowder_Falls), 2024 Integrated Report. Aquatic Life use: not assessed. This is a Clean Water Act assessment-unit classification (the US analogue of WFD), not a live reading.

Status is for the Clean Water Act assessment unit covering this reach.

EPA ATTAINS (Clean Water Act) · MD-02130805-Gunpowder_Falls

The full read · show the working · for Brown Trout · confidence 90%
How the 82 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow80 × 22%17.6
Clarity95 × 18%17.1
Feeding Time55 × 13%7.2
Pressure80 × 7%5.6
Insect activity55 × 12%6.6
Conditions total= 82
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitymodelled from regional profilemodelled
What would change the calculation
The dawn and dusk windows score higher than the midday lull.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout 1 January → 31 December
Related guides
Euro Nymphingsubsurface methods
Booking & contacts