Convert Tributaries and Lakes to Splines and Polygons

Honestly, this is probably a bigger ask than I can imagine. I don't know enough about how tributaries and lakes are defined in the Create Water device. What I do know is that the tributaries and lakes you do get are dependent on the current extents, so if you try to crop out an area and zoom in on a smaller extent the tributaries and lakes you had tend to disappear. I thought I could trace them in a Shapes device and preserve them in that way, but you can't really trace them in the Visual Editor. It tries to update every time you alter a node, wiping out the rendered view you were trying to trace from and dropping you back down to 128 byte resolution. So, either that needs to be changed in some way that preserves the full resolution of the input terrain, or some mechanism for converting the tributaries and lakes into splines and shapes. I'm sort of assuming Create Water is creating and then discarding that kind of data. So I imagine having some way to 'capture' it and use it as Shapes.