All right. Thanks for the suggestion.

I decided after a day of the editor acting up to focus more so on my script for quests/journals, and I went back to the editor in a fresh frame of mind. This time I started off making my river and island in a 3x3 terrain for one like this: https://cdn.discordapp.com/attachments/317162246398803968/366003400418263050/unknown.png

So the question that had not occurred to me was how to actually add water to a level. I see there is an AI Brush tool to add surfaces of water. However, I am not seeing a way to simply add a water level (if that's what it's called). I assumed it there was some surface like lava in the tutorial video.