I "figured" this out after bashing my head against the keyboard for 20 minutes. I'm still not entirely sure how, but I think the key is to make a path from the portal to the Shattered Passage to the 2nd entrance to the Sunken Crown.
Here's how I did it:
1) Exit Sunken Crown using the left portal and drain the pool with the statue
2) Cover up the other entrance to Sunken Crown
3) Exit Drowned Kingdom using the right portal in Sunken Crown
4) Reenter Drown Kingdom and take the first portal to the north
5) Use the statue to drain the northernmost pool
At this point you should be able to make your way to the 2nd Sunken Crown entrance and the pool inside should be drained (at least it was for me.....)
If that doesn't work here are the pools I had drained when I solved the puzzle: the northernmost, the one in the middle of the map, the one with the statue leading to Sunken Crown, and the one with the switch above the first sunken crown entrance
