Quote (SpaceEngineer)
River systems are almost impossible in this procedural approach - they require at least 10,000 iterations of the erosion algorithm per pixel, or some blending with a pre-generated vector mask.
Hm... Perhaps (in the rather distant future, of course) a "render rivers/full detail render" option could be added. This would only effect the selected planet, and would likely disable moving the camera. Basically, one would only use it when they already had a scene set up, just for the extra detail.