How to place river and/or lake in the map editor???

[unmerged(387025)]

I "dig" a hole with editor tools, but I can't fill it with water to create a lake or a river

 

[City Builder]

I believe that all water is at a certain level in the game so one only needs to dig deep enough and water will come. I use the flatten tool and right click on a body of water and then run the tool where I want the new lake or river and water fills it automatically.

I'd love to be able to put water at the top of a mountain but that doesn't seem to be possible, at least not with anything I've tried thus far.

 

[unmerged(387025)]

ok, thanks