Kelp, I did a massive 20 chunk lake took a good few hours but was worth it

I probably should’ve specified that I’m on Education Edition. Sorry if I’ve caused a little bit of confusion! I was kinda rushing when I posted this, so I forgot to include the version.

If each edge block is a source they fill in. But you have to do that for every layer.

Ngl, this looks like art. I say keep it, it’s cool. But if you really need to flatten it, your best bets without commands are either kelp or 1 big layer of blocks right below the water surface.