I finally found a map with a chasm and river really close to each other (and magma+sand, always a necessity) so I could finally make my dream of a dining room with a waterfall through it a reality. Usually draining is a major issue, draining the water into the chasm is a simple and effective solution,
or is it?
Well, I managed to set everything up without flooding the entire fortress- it was nice because the waterfall ran down next to the stairway from the food processing area, so the dwarves were absolutely sure to get a nice thought from the mist. Unfortunately there were... issues:
You might notice that mysterious cloud of miasma there... It's been a near permanent feature of this particular dining room, like a curse, and it's been more than countering the happy thoughts the waterfall was supposed to bring...
It looked as if the cloud was emanating from the grates in the floor... With trepidation, I checked down there to see what might be the source of the foul stench and found a truly gruesome sight. Corpses. Salmon corpses. Dozens of them directly below the dining room, and several more washed further down stream.
What was this? Was there a mercury spill upriver or something?
No.
It was something more sinister, more deliberate.
As I watched the fish rot, stupefied, the true culprits showed themselves. From the mist and miasma emerged: my god damn stray cats! All of them! They had somehow managed to find their way into the drainage system below my dining room, where the water was rather shallow, and were systematically killing all the fish that passed through. That's right- I had a fish-cat infestation.
I've since extracted them, recruiting a peasant to go down and round them up, collecting them all in an aquarium, I've also plugged off all the access shafts to the drainage system, but let this be a cautionary tale: More than mere demons lurk in the deep.