MaineNatural lake, 1,983 acres, Penobscot County
South Branch Lake water level
Latest satellite readingSWOT
000.00ft above sea level
Loading the latest passes from NASA
- Since last pass
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- Past 30 days
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- Past 90 days
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- Passes in 90 days
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Last 90 days of satellite passes
Each dot is one pass of the satellite. Lines between dots are straight, so they do not show what happened between passes.
Recent satellite passes
| Pass | Level (ft above sea level) | Change |
|---|
Reading these numbers
We have not matched South Branch Lake to a public level gauge, so these readings come from SWOT (Surface Water and Ocean Topography), a satellite run by NASA and the French space agency CNES since 2022. On each pass its radar maps the whole lake surface and reports one water surface elevation for it. NASA publishes the results through its Hydrocron service, and this page reads them live, keeping only passes that NASA flags as good or acceptable.
The satellite does not pass every day. Most lakes are measured every 10 to 21 days, sometimes twice in a few days, and a pass can be dropped when heavy rain, ice or a steep shoreline confuses the radar. The date of each pass is shown with its number, so you always know how fresh it is.
Each reading is the height of the water above sea level (the EGM2008 geoid), usually good to within half a foot on a lake this size. That is a different reference from a staff gauge on a dock or the "full pool" number a dam operator quotes, so the figure here may sit a foot or two away from theirs even when both are right. Use it for the trend: whether the lake has risen or fallen since the last pass, and by how much.
Natural lake levels usually move slowly, following rain, snowmelt and evaporation. A rise after a wet week can flood low docks and beaches, while late-summer lows expose rocks and weed beds near shore.
South Branch Lake water level questions
How is the South Branch Lake water level measured?
By NASA's SWOT satellite, which measures the height of the lake surface from orbit on each pass. We have not matched South Branch Lake to a public level gauge, so the satellite is the measurement we can show for it.
How often is the South Branch Lake water level updated?
Whenever the satellite passes over and gets a clean reading, usually every 10 to 21 days. NASA posts each pass within a few days, and this page picks it up as soon as it is published, so there is no need to wait for a site update.
How accurate is the satellite water level?
On a lake this size a single SWOT pass is usually good to within half a foot. NASA flags passes that are less reliable, and we leave out every pass it marks as degraded, any suspect pass that saw only part of the lake, and any with a large stated error. It is accurate enough to see a lake rise after heavy rain or drop through a dry summer, but not to judge a few inches of clearance at a ramp.
Why is this number different from the marina or operator's level?
The satellite reports height above sea level using the EGM2008 reference surface. Gauges on docks and dams often use a local reference point or an older survey datum, so the two can differ by a foot or more. Compare changes over time rather than the raw numbers.
Nearby lakes
If South Branch is blown out, these are the closest alternatives. Tap through for their water levels.