You can terraform lakes

[allocater]

You can terraform any lake by building buildings right next to it and building connections along-side it. Neighboring vertices and all connection vertices will be raised to the normal level, reducing the lake step by step.

Here is a timelapse:

http://imgur.com/a/v1m06

[Jatlen]

You can also terraform hills and mountains. ^^

[thetraveler]

Mines are particularly useful for mountain moving ;-) Total bug/hack though... I wish they would just make terrain modification a real part of the game.

[Instructor]

I've noticed that too! nice

[Instructor]

Can you show me how to remove hills?

[Jatlen]

There is a thread of 16th August about that topic:
http://steamcommunity.com/app/403190/discussions/0/353916981476507405/

Be careful if you place airlocks in regions where there is supposed to be a mountain, sometimes bots/colonists take strange routes then (travelling up/down or right/left). And don't reload your game as long as you haven't used that new space. After reloading your terraforming is gone.

[Instructor]

thanks