The default bodies of water, specifically lakes, reservoirs and reservoirs originate from the massive database that is OpenStreetMap. It should be noted that as regards the “natural = water” they are 100% surfaces covered by water while the “landuse = reservoir” are 95% dry (intermittent), while in the Simulator they are always water surfaces.
In order not to have water surfaces everywhere even where there is none, you could have an option to exclude that water polygon already during the data acquisition phase from OSM.
If you want, it is possible to exclude that water polygon now with a dedicated polygon, I’m fine with one but when are there many more than one?
OpenStreetMap wiki related to "landuse = reservoir
