Potomac River at Little Falls, MD
USGS gauge 01646500 · drainage 11,560 sq mi · observed Oct 16, 9:50 PM EDT · 30 min old
Last 7 days Live gauge
Source: USGS Water Data API (continuous values), observed to Oct 16, 9:50 PM EDT. Shaded band: 25th to 75th percentile of USGS daily statistics for each date; dashed: median. Flow in cfs.
Rate of rise and fall Live gauge
| Window | Flow then | Change to latest | Gage height then | Gage height change |
|---|---|---|---|---|
| 1 h | 9,680 cfs | ▬ +0.00 cfs (+0.0%) | 3.94 ft | +0.00 ft |
| 3 h | 9,960 cfs | ▼ -280 cfs (-2.8%) | 3.97 ft | -0.03 ft |
| 6 h | 10,300 cfs | ▼ -620 cfs (-6.0%) | 4.01 ft | -0.07 ft |
| 12 h | 11,000 cfs | ▼ -1,320 cfs (-12.0%) | 4.08 ft | -0.14 ft |
| 24 h | 13,400 cfs | ▼ -3,720 cfs (-27.8%) | 4.32 ft | -0.38 ft |
Last 7 days
| Measure | Flow | Time | Relative to latest reading |
|---|---|---|---|
| Highest reading | 24,300 cfs | Oct 14, 10:45 AM EDT | 59 h earlier |
| Lowest reading | 1,330 cfs | Oct 10, 6:10 AM EDT | 160 h earlier |
Source: computed from USGS continuous readings (Water Data API) to Oct 16, 9:50 PM EDT. Each row compares the latest reading with the reading closest to that many hours earlier; the arrow is steady (▬) when the change is within 1%.
Daily mean flow Live gauge
| Date (gauge-local) | Mean flow | Note |
|---|---|---|
| Oct 16, 2026 | 11,042 cfs | |
| Oct 15, 2026 | 16,182 cfs | |
| Oct 14, 2026 | 21,889 cfs | |
| Oct 13, 2026 | 12,366 cfs | |
| Oct 12, 2026 | 9,638 cfs | |
| Oct 11, 2026 | 3,487 cfs | |
| Oct 10, 2026 | 1,494 cfs | |
| Oct 9, 2026 | 1,434 cfs | |
| Oct 8, 2026 | – | Partial day |
Source: USGS Water Data API (continuous values); each mean uses readings on that gauge-local date, shown only with at least 80% of expected readings.
The same 50 days in earlier years Historical record
━ 2026 ╌ 2025 ╌ 2024 ╌ 2023
| Year | Mean flow | Highest day |
|---|---|---|
| 2026 | 3,400 cfs | 22,100 cfs |
| 2025 | 1,704 cfs | 2,760 cfs |
| 2024 | 6,655 cfs | 38,100 cfs |
| 2023 | 1,742 cfs | 5,510 cfs |
Source: USGS daily mean flows (Water Data API). Each line is the 50 days from Aug 27 to Oct 15, shifted to the same calendar dates in earlier years; gaps are days without a published value. Recent days are provisional.
Compared with this gauge’s record Historical record
| Measure | Value | When or rank |
|---|---|---|
| Peak daily flow, last 7 days | 22,100 cfs | Oct 14, 2026 |
| Last time daily flow was this high or higher | 22,200 cfs | May 31, 2026 (4 months earlier) |
| Last day above the 90th percentile for its date, before this peak | May 30, 2026 | 5 months earlier |
| Days above the 75th percentile for their date | 6 of 30 | last 30 days |
| October 1 to 15, mean flow | 5,530 cfs | rank 28 highest of 97 years |
| Peak daily mean compared with annual instantaneous peaks of record | Below the lowest of 95 | lowest annual peak 30,600 cfs |
Source: USGS daily mean flows (Water Data API), 1930 to 2026 (35,293 days), data through Oct 15, 2026, computed 2026-10-17; method record-v1. Percentiles are USGS daily statistics. Recent days are provisional.
Largest annual peaks Historical record
Ten largest peaks of record
| Date | Peak flow | Gage height at peak |
|---|---|---|
| Mar 19, 1936 | 484,000 cfs | 28.10 ft |
| Oct 17, 1942 | 447,000 cfs | 26.88 ft |
| Jun 24, 1972 | 359,000 cfs | 22.03 ft |
| Apr 28, 1937 | 347,000 cfs | 23.30 ft |
| Jan 21, 1996 | 347,000 cfs | 19.29 ft |
| Nov 7, 1985 | 317,000 cfs | 17.99 ft |
| Feb 16, 1984 | 222,000 cfs | 13.73 ft |
| Aug 20, 1955 | 216,000 cfs | 17.60 ft |
| Oct 11, 1976 | 208,000 cfs | 13.18 ft |
| Feb 26, 1979 | 206,000 cfs | 13.12 ft |
Five most recent annual peaks
| Date | Peak flow | Gage height at peak |
|---|---|---|
| May 16, 2025 | 156,000 cfs | 11.72 ft |
| Apr 5, 2024 | 94,100 cfs | 9.20 ft |
| Dec 24, 2022 | 44,800 cfs | 6.59 ft |
| May 9, 2022 | 118,000 cfs | 10.16 ft |
| Mar 3, 2021 | 97,600 cfs | 9.27 ft |
Source: USGS annual peak streamflow (Water Data API), 95 annual peaks, 1931 to 2025. A water year's peak is its highest instantaneous flow.
Historic crests Official NWS
| Date | Crest stage | Flow |
|---|---|---|
| Mar 19, 1936 | 28.10 ft | 484,000 cfs |
| Oct 17, 1942 | 26.88 ft | 447,000 cfs |
| Apr 27, 1937 | 23.30 ft | 347,000 cfs |
| Jun 23, 1972 | 22.03 ft | 359,000 cfs |
| Jan 21, 1996 | 19.29 ft | 347,000 cfs |
| Nov 6, 1985 | 17.99 ft | 317,000 cfs |
| Sep 8, 1996 | 17.84 ft | 314,000 cfs |
| Aug 19, 1955 | 17.60 ft | 216,000 cfs |
| Oct 29, 1937 | 15.62 ft | 181,000 cfs |
| May 13, 1932 | 15.25 ft | 168,000 cfs |
Source: National Weather Service forecast point BRKM2 (Potomac River near Washington DC (Little Falls)), historic crests as published by the NWS; the NWS may have recorded them on an older gauge datum. The USGS annual peaks above are a separate record and can differ in date, flow and datum.
Gage height to flow rating Historical record
Line: current USGS rating, gage height (ft, horizontal) to flow (cfs, vertical). ● latest reading, 3.94 ft and 9,680 cfs.
Source: USGS rating table for the gauge (NWIS rating depot, expanded shifted rating, 4,000 rows, thinned to 92 points), fetched Oct 16, 10:12 PM EDT. Ratings are provisional and change with the channel.
Water temperature by month Historical record
Source: USGS daily mean water temperature (parameter 00010, Water Data API), 1988 to 2026, mean of all published daily values in each calendar month (days counted under each month; (few) means fewer than 150 daily values).
Water quality sensors Live gauge
| Measure | Latest value | Observed |
|---|---|---|
| Water temperature | 66.6 °F (19.2 °C) | Oct 16, 9:50 PM EDT |
| Dissolved oxygen | 9.4 mg/L | Oct 16, 9:50 PM EDT |
| Turbidity | 10 FNU | Oct 16, 9:50 PM EDT |
| pH | 8.0 pH units | Oct 16, 9:50 PM EDT |
| Specific conductance | 275 µS/cm | Oct 16, 9:50 PM EDT |
| Nitrate plus nitrite | 1.2 mg/L | Oct 16, 9:30 PM EDT |
Source: USGS Water Data API (continuous values). Values as reported by the gauge, provisional.
Flood stages Official NWS
| Category | Gage height (ft) |
|---|---|
| Action | 5.0 ft |
| Minor | 10.0 ft |
| Moderate | 12.0 ft |
| Major | 14.0 ft |
Source: National Weather Service forecast point BRKM2 (Potomac River near Washington DC (Little Falls)), fetched Oct 16, 10:16 PM EDT. Compare with the gage height above; thresholds belong to that forecast point.
Flood impacts by stage Official NWS
| Stage | National Weather Service impact statement |
|---|---|
| 3.5 ft | The river reaches caution level for boaters, as defined by the State of Maryland. Fast moving water and changing currents will be experienced. |
| 4.5 ft | The river reaches danger level for boaters, as defined by the State of Maryland. Conditions for boating will be extremely hazardous. |
| 5.0 ft | Portions of the Potomac Heritage Trail begin to flood. Water begins to affect portions of the Billy Goat Trail between Great Falls and Carderock. These trails will be closed. |
| 5.5 ft | Water reaches the top of the ferry landing for Sycamore Island. Ferry service to the island will likely be suspended. |
| 7.0 ft | Upper portions of the River Trail at Great Falls National Park begin to flood and will be closed. |
| 9.0 ft | Several trails on both sides of the river between Great Falls and the Chain Bridge are flooded and will be closed. |
| 10.0 ft | Water begins to overflow the banks into low lying areas on the Maryland side of the river near Little Falls. Water begins to enter the canoe shed at Sycamore Island. |
| 11.0 ft | Water covers the towpath between Swains Lock and Pennyfield Lock, mileposts 17 to 19 on the C&O Canal. |
| 11.5 ft | Water covers the towpath in multiple spots between the Washington Aqueduct Dam and Pennyfield Lock, mileposts 15 to 19 on the C&O Canal. |
| 12.0 ft | The C&O Canal overflows at the Great Falls Tavern. Water covers the towpath in many areas. |
| 14.0 ft | Significant portions of the C&O Canal towpath are flooded. The Blockhouse Point Park is flooded. Water reaches the retaining wall at Overlook 1 at Great Falls National Park but does not overtop it. |
| 15.0 ft | Most of the C&O Canal towpath from Pennyfield downstream is flooded. |
| 16.0 ft | Water reaches the clubhouse on Sycamore Island. |
| 17.0 ft | Water overflows the overlooks at Great Falls National Park and approaches the lower level of the visitors center. Most of the C&O Canal towpath downstream of Pennyfield is flooded. There is approximately a foot of water in the clubhouse on Sycamore Island. |
Source: National Weather Service forecast point BRKM2 (Potomac River near Washington DC (Little Falls)). Statements are quoted from the NWS and describe that forecast point.
Sources and method
- Data: U.S. Geological Survey. Terms
- River forecasts and flood stages: National Weather Service. National Water Model guidance: NOAA. Terms
USGS daily statistics, downloaded 2026-10-12
Percentile method: trailing 24 h mean vs USGS daily percentiles for calendar date 10-16.
Percentile is estimated from USGS published daily percentiles. Readings are provisional until USGS reviews them. Not endorsed by USGS, NOAA or the National Weather Service. Not for navigation or safety-of-life decisions; the absence of an alert is not a statement that conditions are safe.