About this river
Saint Marys River is an 11.4 mile river near Chesapeake Bay Charters in Maryland. Streamflow is measured at the USGS gauge St Marys River at Great Mills, MD (site 01661500). The National Hydrography Dataset places it at stream order 5. Reach geometry comes from the USGS National Hydrography Dataset.
Typical flow by month
1946 to 2026
Saint Marys River typically runs highest in March, at a median 24 cfs, and lowest in September, at 4.1 cfs. The highest flow on record for any single day is 2,650 cfs, in 1999.
| Month | Typical (cfs) | Usual range (cfs) | Relative level |
|---|---|---|---|
| January | 19 | 12 to 32 | |
| February | 21 | 14 to 38 | |
| March | 24 | 15 to 43 | |
| April | 22 | 14 to 33 | |
| May | 13 | 8.9 to 23 | |
| June | 8.8 | 5.1 to 16 | |
| July | 5.9 | 3.5 to 11 | |
| August | 5.5 | 3.3 to 11 | |
| September | 4.1 | 2.9 to 8.8 | |
| October | 5.9 | 3.8 to 12 | |
| November | 9.7 | 6.5 to 18 | |
| December | 16 | 9.5 to 29 |
Typical is the median of each month’s daily median values, and the usual range runs from the median 25th to the median 75th percentile, across about 79 years of record. Statistics published by the US Geological Survey for St Marys River at Great Mills, MD (site 01661500). Conditions on any given day can fall well outside the usual range. Check the current reading before you go.
Boat access nearby
3 mapped launches sit in the mapped area of Saint Marys River, all of them public access. Ramp data comes from the USGS national boat-ramp inventory.
Embed this gauge on your site
Paste this snippet anywhere, an outfitter page, a club site, a trip report, to show Saint Marys River's live streamflow, water level and 7-day trend. It reads the USGS gauge directly, updates itself, and links back here.
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