Blog · September 27, 2026
Ordinary High Water and the Lot Line
Ordinary high water is a water-law boundary, the usual high level of a lake or stream, not the line of today's waves.
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When a plat or deed calls to ordinary high water, the boundary is that elevation or mark. A flood event above it is not a new line.
On the recorded sheet
Surveyors look for the vegetation and debris evidence the courts in that state use. A GIS blue fill is a map symbol.
The mix-up to avoid
Do not confuse a FEMA flood elevation with ordinary high water. One is an insurance map. The other can be a title boundary.
Find the county map
Search the county on the Platbookmapper home page. The directory links to the official parcel viewer. It does not draw the lots, and the line on the screen is an assessment map, not a survey.
Not a survey. County GIS and tax parcel maps are assessment and planning layers. They are not a substitute for a recorded plat, deed, or licensed survey.