So after a few mishaps with irrigation (sometimes too much water, sometimes not enough) I decided to install a floodgate in the murky pool that would put mud on my fields. I then noticed that the murky pool was one square away from a river, and figured "Hey! I can make a bigger room if I install another floodgate in the river!" Surprisingly, despite this being one of my first forts (I tend to abandon after a couple of years when I'm dissatisfied with the layout, rather than anything going terribly wrong. Still learning the ropes, so I figure they don't count), I didn't mess up that too badly. I had the forethought to put a door in the entrance to the rest of the fort, forbade the door and made sure it was pet proof. And I made sure there were no dwarfs in the room.
So I had the future farming area nice and wet. Only I let in a little more water than I meant to, and had 3/4 water in about four 11x11 rooms. Oops. I just had to wait for it to drain, right? No big deal. I closed both floodgates and everything was fine.
Then a few seasons pass, and the water doesn't seem to be draining. I'm a little concerned, but I the caravan came and I wasn't worried for food or booze. Winter comes, and the murky pool freezes over. I suddenly have the great idea to drain the pool, by carrying out the ice, and opening the floodgate so my farm would drain into the murky pool, freeze, and I'd carry it out.
So I start channeling the ice from above (after I notice that mining it from below didn't work and I didn't want to open the floodgate). Immediately my miners get to work and I receive the message "Urist McLegendaryMiner has been encased in ice!"
What?!
I still don't know how that happened. The rest of the dwarfs kept on mining the ice happily. All the water was ice. I don't know how he managed to freeze himself in ice, since the wiki said that happened if they were in water as it froze. Die and learn, I guess. The fortress was really coming together, too. Save for the farm.
I started another one shortly after. Such a pointless death.