https://www.youtube.com/watch?v=pfonMfP__Ks
In open source field there is Mantaflow that available in Blender, but it's of course not solution for real-time.
The effect: https://29a.ch/sandbox/2012/terrain/
The slides that explain: https://29a.ch/slides/2012/webglwater/
https://www.youtube.com/watch?v=55rsJI11FOA
http://physicsforests.com/
https://www.youtube.com/watch?v=pfonMfP__Ks
In open source field there is Mantaflow that available in Blender, but it's of course not solution for real-time.