I installed SDK and I can see the problem. When I use TFMViewer to look at the area and right click the properties, I can see that the stored information at that point suddenly changes from WaterPoly with Shoreline property to the Stream property. The stream property is not displayed in the game, so the river water ends abruptly before getting to its origin. Wider areas of the river are disjointed and appear as independent water bodies.
FS 9 had the same issues with its water areas.
I can't figure out how to edit those properties to set the stored data identifiers from Stream back to the Waterpoly and Shoreline that it needs to be in order to continue the river water on.
0302 / 2916 north to 0301 / 2915. Southern Maine USA.
Most aggravating that they would do that. The Stream path is actually in the correct place where the Waterpoly and Shoreline river should be propertied to continue along that water route.
Hope I explained this right because it will take a smarter person than I am to fix it if it isn't done by point and click on the map areas and change some text. It seems like a person could probably make the necessary edits if there was some way to de-complile and then re-compile the existing bgl's to change those property points.