Texturing with lakes and rivers

The river/lakes texturing is done through PCG and is global to the whole world, it spawns smaller masks along the lakes and rivers. The mask used is the same as the Auto Landscape Mask and therefore shares the same properties.

You have an example material with Massive World called MI_Riverbed

Customizing the material

Duplicate the MI_Riverbed, go inside BP_Rivedbed blueprint then in class-default, switch the Material for the new one you want to use.

For advanced users

In your scene, there is a BP_MassiveWorld actor. In it, there is a PCG component holding a PCG graph called "PCG_Road_Water". Feel free to duplicate it and replace the graph if you want to create your custom logic.