Uh... this again?
Yep, this again.
So, what did I do?
After some trial and error (saving beforehand) I was able to figure out where I had to approach from to trigger the water blocks to fall, and began building a catchment to catch them.
It took a while,
Distracted doesn't matter while building though, and the lag for anything but switching to build mode was awful.
Unfortunately the water was right up against the south edge of my camp, preventing me from building on several tiles there.
So I did the obvious thing.
I made some magma-safe minecarts, fast-travel to a volcano north of me, swim down inside, then find the nearest candy-cane so I can drop the carts without the magma flows eating them.
Stand on a candy ledge, get my needs filled, fill up my backpack with magma, swim back, travel home. Drop minecart loads of magma onto the suitable locations. Did this dozens of times to cast it all. Magma is heavy.
Once I got those holes plugged, I noticed the water was overflowing out of the side and I needed more wood to prevent it, so I went over there to do some logging.
Uh... hmmm.
The red stuff isn't blood btw, it's bitter ooze, the southwest chunk of the map is on an evil mountain that the river runs through, which I assume causes the glitchy teleporting water blocks stuff.
So I've got about 40,000 tiles of water, the bottom ~24,000 are 7/7, the top I've been chucking water from the river in with minecarts to fill it from 4/7 up to 7/7, and then I guess I'm gonna build an aqueduct going north.