>>62971639Here's a very basic guide. There are source blocks and flow blocks. Source will spread to produce flowing water. If enough water flows into a block, it turns into a source.
You can then apply this basic rule to the fact that the entire ocean is a solid mass of source blocks. When you start making source blocks spontaneously vanish with sponges, which spots are safe? Which spots can be cleared permanently, which turn into flowing, and which ones are transformed right back into source from water filling it back up? The answer is that nobody is willing to puzzle this shit out unnecessarily, which is why you need to cordon off areas and completely drain them.