My render distance is 10 chunks (160 blocks), so, an 80x80 area should not be a problem.
The problem is that the blocks are standing statics in the middle air, even if the fill comand covers all the zone, the water blocks also can't be removed with sponges, the only way to remove them is replacing it with another block (dirt, stone, etc)
Okay, thanks for your attention! 🙂