Moderate Flood
248 ft
Current Water Level
Gage Height
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Streamflow
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Last Reading
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This is an NWS forecast point (LID: LMRV2). Live data may be limited. View on NWS AHPS →
FLOOD STAGES
Know the flood categories.
Flood stages defined by the National Weather Service. Gage height data from USGS Water Resources.
Minor Flood
240 ft
Action Stage
220 ft
What Floods at Each Level
252 ft
Water starts to overtop the Lake Mercer Dam.
248 ft
Flooding of structures is possible if water enters lower levels of homes along Golden Sunet Lane, Daum Court, and Galla Knoll Circle.
245 ft
Lake water may approach the back of some homes, especially along Golden Sunset Lane, Daum Court, and Galla Knoll Circle.
240 ft
Lake water may approach a cul-de-sac on Wagon Trail Lane. All trails in Lake Mercer Park are likely flooded.
234 ft
Dam's auxiliary spillway is activated which may cause swift water to flood nearby downstream trails.
220 ft
Backwater lake flooding likely starts to affect canoe ramps, trails, and gated service roads in Lake Mercer Park.
Impact statements from the National Weather Service, describing what typically happens at each water level.
7-Day Water Level Chart
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Historic Crests
| Date | Stage | Flow |
|---|---|---|
| Sep 9, 2011 | 228.03 ft | — |
About This Gauge
NWS LID
LMRV2
River
South Run
County
Fairfax, VA
Coordinates
38.7378°N, 77.2547°W
Get Flood Alerts for South Run
StormCast monitors this gauge and sends a push notification to your phone when the water level crosses into a new flood category — even at 3 AM.
Frequently Asked Questions
What is the current water level of South Run at Lake Mercer?
The South Run at Lake Mercer gauge is maintained by USGS and reports water levels every 15 minutes. Visit this page to see the latest reading updated live, or download StormCast to get push alerts when levels rise.
What is flood stage for South Run at Lake Mercer?
The NWS-defined flood stage for South Run at Lake Mercer is 240 feet. Action stage begins at 220 feet. Moderate flooding starts at 248 feet, and major flooding at N/A feet.
How do I get alerts when South Run rises?
Download StormCast free on Google Play, go to River Gauges, and add South Run at Lake Mercer to your watchlist. StormCast will send a push notification to your phone whenever the water level crosses into a new NWS flood category.
Where is the South Run at Lake Mercer gauge located?
The gauge is located in Fairfax County, Virginia at coordinates 38.7378°N, 77.2547°W. Data is provided by the U.S. Geological Survey and the National Weather Service.
More Resources
Source & Notes
- Stage may be affected by ice.