It seems to be very fiddly in terms of z position. Try moving your landscape up and down. I haven’t managed to get it working on large landscapes, but it should work on smaller ones.
Other steps I took:
- Make sure you enable edit layers
- I made a new edit layer “water”, and made sure it was selected in while in landscape mode, when I dragged in the water body.
You should also automatically get a brush actor spawned, which you can control in the world outliner.