If you are aware, or readed, the N threads about underwater civs, you know that is imposible for these to reach late society, industrial, and space stage, so, that leave us with amphibious civs being the only way to have almost an aquatic civ.
We can classify these civs as “true amphibious”, and “fake amphibious”.
These civs are composed by creatures that can live in water and land at the same time. We can classify these acording to their origins,
The creatures of this civ evolved from the first creatures that ventured into land. Instead of abandoning water completely, these creatures didn’t cut all their ties with this element.
These civs are composed of creatures that evolved on land, but “decided” to return to the water. Like the “water first”, these creatures didn’t cut their ties with their home enviroment , in this case, “land”
These civs are composed of creatures that are well adapted, and live entirely in one enviroment, but can visit the other one. They can be classify acording to their home enviroment:
These are full-aquatic creatures, that have to go to dry land to get resources that can’t be get underwater, like metals.
These are full-terrestrial creatures, that have to go to water to get food, or other materials found underwater.
each of this civs will have their own problems, and challenges, but they are more plausible that full-underwater civs. If you don’t believe it, just publish in reddit a scientific paper with proof that underwater civs are plausible (and maybe we can have waterworlds, or hycean planets as home of our creatures)