*In the cave leading to the dungeons of Fort Joy that is infested with fire slugs, there is a pond in the main area containing most of the slugs. While that pond looks like it is filled with water, the game does not fully recognize it as such. Moving a burning character into the water does not extinguish the fire.
This is something that has existed since previus game.
I think it has to do that lake, rivers, waterfall etc is part of the enviroment while the things you interact with like oil and self produced water is coded differently.
I agree they should try find a way to fix that, it is always jarring to have fire burning beneath a river, but i think it is a difficult task for them.
