I think it is known on the mantis. Or at least it should be, since it's been around for a LONG time.
I may well end up having to leave the fortress designed specifically to be flooded, and prevent the water from moving around as much as possible so it minimizes the hit to your FPS. It probably wont be 100% effective at stopping the water flow. Other ideas include draining it all away into the caverns, which would butcher your FPS, or setting up some elaborate means to set fires throughout the fortress to evaporate it away, which would butcher your FPS. Or ask really, really nicely for a proficient dfhack scripter to write a script which, like, removes all the water or some shit. Dfhack's liquids command, setting the entire map to 1/7 water would technically work but you'd probably have to reveal the map to do it and any empty spaces where water was floating in mid-air like the caverns would have to calculate paths down and flow around until they equalize, which would still hurt your FPS.
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I'm trying to upload the save at the moment. It may take a while, I suppose.
I did manage to increase the FPS upon visiting the site by sealing off most of the water outlets. It no longer threatens to burn down my rig, so hopefully nobody else will die of old age exploring.
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Here's the save:
http://www.mediafire.com/download/bi6gfd5asfpr8kk/The+Museum+-+Turn+58c.7zLet me know if anything goes horribly wrong.