TidalMapSt Marys River at Great Mills, MD Water Level Today
NWS river forecast
| When | Stage | Flow |
|---|
Forecast from the NOAA National Water Prediction Service. Issued a few times a day and only while a forecast is active. Not for navigation.
Last 30 days
About this gauge
USGS gauge 01661500 sits on the St Marys River and reads everything draining 24 square miles of the Lower Potomac basin. Its datum sits 6 feet above sea level NAVD88. Daily flow has been on record here since 1946, 79 years of it.
Normal flows here
The St Marys River runs a median of 12 cfs at this gauge across 79 years of record. March is the fullest month at a median 24 cfs, and September the leanest at 4.1 cfs. The highest daily mean on record is 2,650 cfs in 1999, and the lowest is 0.2 cfs in 1999.
| Month | Median flow | Share of annual median |
|---|---|---|
| Jan | 19 cfs | 158% |
| Feb | 21 cfs | 175% |
| Mar | 24 cfs | 200% |
| Apr | 22 cfs | 183% |
| May | 13 cfs | 108% |
| Jun | 8.9 cfs | 74% |
| Jul | 5.9 cfs | 49% |
| Aug | 5.5 cfs | 46% |
| Sep | 4.1 cfs | 34% |
| Oct | 5.9 cfs | 49% |
| Nov | 9.7 cfs | 81% |
| Dec | 16 cfs | 133% |
Medians from the USGS daily-statistics record, 1946 to 2026. A month at 100% is running at its own long-term median.
Flood stages and record crests
The St Marys River reaches flood stage at this gauge at 7 feet. NWS starts watching it at 5 feet. The highest crest on record is 13.3 feet, in August 1969.
| Category | Gage height |
|---|---|
| Action | 5 ft |
| Minor flooding | 7 ft |
| Moderate flooding | 8 ft |
| Major flooding | 10 ft |
| When | Crest |
|---|---|
| August 1969 | 13.3 ft |
| August 2011 | 13 ft |
| September 1999 | 12.8 ft |
| July 1960 | 12.1 ft |
| August 1955 | 11.8 ft |
Flood categories and crest history from the NOAA National Water Prediction Service, gauge GMRM2. Stages are gage height, not depth. Not for navigation.
Nearby river gauges
- Mcintosh Run near Leonardtown, MD
- St Clements Creek near Clements, MD
- Zekiah Swamp Run near Newtown, MD
- Piscataway Creek near Tappahannock, VA
- Western Branch at Upper Marlboro, MD
- Dragon Swamp at Mascot, VA
- Piscataway Creek at Piscataway, MD
- Mattawoman Creek near Pomonkey, MD
- Chicamacomico River near Salem, MD
- Patuxent River near Bowie, MD
- Mattaponi River near Beulahville, VA
- Beaverdam Creek near Cheverly, MD
Live streamflow and gage height: USGS gauge 01661500. Percentile context computed against the gauge's period of record. Not for navigation.
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