I started underwater, created one level at a time. going in a clockwise circle placing an assortment of rubble and picked up grass and dirt. Draining the water was the hardest part. I made a mistake and sometimes put sponges in front of holes, which flooded the whole maelstrom again as I was deleting. I learned two things from doing this.
1: don't put a sponge in front of a hole
2: delete sponges up to down