Beneath the ever-rising sea, there live pesky marine creatures intent on destroying all of your consorts' hard work. This land has been built and rebuilt hundreds of times over in an effort to keep it above the waterline, with ancient drowned cities left behind in the deep. It will continue to be so until the world basin is finally drained.
So, you're not just on construction duty, you're on "fish" duty too. Haniel did say he liked them, so you guess it makes sense that's what you're up against. This really is a lot like how things go back on Repiton, only with marginally less risk.