Watermasking tool watermask produces land and water polygons that replace stock seas, lakes and rivers. Given a border that defines the area you want to replace, and water polygons, it will build a MSFS terrain shapefile that you can directly add to your project. The resulting files are best placed into a separate project component (BGL type).
You should generate custom mesh for the same area (with elev tool), otherwise you will see mesh artifacts.
This is an experimental tool. Inspect the resulting water bodies for processing errors.
msfs watermask [-help] [-formats] [-border filemask] [-water filemask] shp
Shows a list of all currently supported file formats.
-border <filemask> [<filemask> …]
One or more vector polygon files that define the area to replace (wildcard supported).
-water <filemask> [<filemask> …]
One or more vector polygon files that define water bodies within the replacement area (wildcard supported).
Output ESRI Shapefile. MSFS XML metadata file will be added to it automatically.
Load polygons from water.shp, cut them to area.kml and write to watermask.shp as MSFS terrain shapefile:
msfs watermask -border "C:\MyLandscape\area.kml" -water "C:\MyLandscape\water.shp" "C:\MyLandscape\PackageSources\watermask\watermask.shp"
See Custom landscape tutorial for a fully featured example.