[2020] Idea: Cave diving biome?

My son had the idea for a flooded cave biome while we groused over a bad low O2 mission and I think it is a really good. Idea. It would be cool to have small chunks of flooded tunnels to swim through and underground lakes. I can imagine swarms of amphibious bugs emerging from the water or water leech tentacles dragging teammates into the deep. Plus the disorientation factor of cave diving is a nice mechanic. Getting the water to flow as holes are drilled may be hugely difficult though. Maybe an expansion idea someday.