Underwater farming/buildings

Right now things being underwater can make large areas completely unusable beyond movement. While I understand the strategic balancing act of deciding build area vs. reservoirs, you can already mostly counteract that by building on platforms and keeping land building-free for farming purposes. So, it would be rather nice to get some utility out of having some things underwater instead, and it would make sense considering the diets and habits of beavers in reality.
Perhaps part of a unique faction that's closer to the species' roots, even.

The main uses as I would see it for this kind of feature:
- Farming seaweed and other submerged plants for food production (Low yield/long growth times as a balance element?)
- Housing, Storage, Labor and Research (Higher resource cost compared to regular buildings?)