Hello everyone, I have recently been wondering what the best way to make things like rivers, paths, and other things like that? I am currently just using a big rectangle for a lake, but what about things that are irregularly shaped? What is the best way to go about doing this? Thanks ahead of time!
You use splines for such kind of stuff -> just use the erosion tool to create the river and then add some splines. 
A 2nd way is to expor the heightmap (with the river part) - import it into a 3d program - create a river mesh - import it - place it on the terrain