I think 'kwelders' are the pieces of land reclaimed from the mudflats, by making small dikes. Probably 'schorren' is a better word. This is supposed to be a test for a Viking time landscape, so around 700AD, with people trying to get a foothold on fertile land. Inland needs more stuff, like maybe areas of shrubs and woods, and perhaps small villages, don't know yet.
Water is not by water shader, btw, but by default shader and reflective. Was faster