St Marys River at Great Mills, MD
USGS Site No: 01661500 • St Marys River • St. Mary's County, MD
St Marys River at Great Mills, MD on the St Marys River is currently at 4 cfs (Low — 12th percentile for this date) . Gage height: 1.37 ft.
Reading from
Historical Percentile Comparison
Today's discharge compared to the long-term record for June 11 at this station. Percentile rank shows what fraction of historical years had lower flow on this date.
| Percentile | Label | CFS Threshold | Today's Flow |
|---|---|---|---|
| 10th | Very Low threshold | 3 | |
| 25th | Low threshold | 5 | Today: 4 cfs |
| 50th (Median) | Normal (median) | 9 | |
| 75th | High threshold | 16 | |
| 95th | Very High threshold | 68 |
30-Day Hydrograph
Recent discharge plotted against the historical 10th–95th percentile envelope for the same calendar days. Source: USGS daily values + long-term statistics.
30-Day Flow History
| Date | Discharge (CFS) | Gage Ht (ft) |
|---|---|---|
| May 28, 2026 | 6 | — |
| May 27, 2026 | 6 | — |
| May 26, 2026 | 6 | — |
| May 25, 2026 | 6 | — |
| May 24, 2026 | 9 | — |
| May 23, 2026 | 12 | — |
| May 22, 2026 | 5 | — |
| May 21, 2026 | 4 | — |
| May 20, 2026 | 2 | — |
| May 19, 2026 | 2 | — |
| May 18, 2026 | 2 | — |
| May 17, 2026 | 3 | — |
| May 16, 2026 | 3 | — |
| May 15, 2026 | 3 | — |
| Apr 21, 2026 | 4 | — |
| Apr 20, 2026 | 5 | — |
| Apr 19, 2026 | 5 | — |
| Apr 18, 2026 | 4 | — |
| Apr 17, 2026 | 5 | — |
| Apr 16, 2026 | 5 | — |
| Apr 15, 2026 | 5 | — |
| Apr 14, 2026 | 7 | — |
| Apr 13, 2026 | 8 | — |
| Apr 12, 2026 | 6 | — |
| Apr 11, 2026 | 7 | — |
| Apr 10, 2026 | 7 | — |
| Apr 9, 2026 | 7 | — |
| Apr 8, 2026 | 7 | — |
| Apr 7, 2026 | 9 | — |
| Apr 6, 2026 | 13 | — |
Station Information
- USGS Site No
- 01661500
- State
- MD
- County
- St. Mary's County
- Coordinates
- 38.2418, -76.5037
- Drainage Area
- 24 mi²
- Datum (ft)
- 6.4
- HUC Code
- 020700110901
Flood Stage Thresholds
- Action Stage
- 5.0 ft
- Flood Stage
- 7.0 ft
- Moderate Flood
- 8.0 ft
- Major Flood
- 10.0 ft
Currently 5.63 ft below flood stage.
Recent Extremes
- Max discharge
-
295 cfsJul 15, 2025
- Min discharge
-
2 cfsMay 20, 2026
- Days at flood stage
- 0
Computed from the local daily-values archive.
Nearby Gauges
-
St Clements Creek Near Clements, MDLow13.6 mi · 2 cfs
-
Zekiah Swamp Run Near Newtown, MDLow28.7 mi · 9 cfs
-
Piscataway Creek Near Tappahannock, VANormal33.2 mi · 12 cfs
-
Chicamacomico River Near Salem, MDLow38.6 mi · 6 cfs
-
Mattawoman Creek Near Pomonkey, MDNormal38.7 mi · 2 cfs