That's the problem with the way civ's borders and pops work. Water heavy cities must be competetive.
But in real life there is no infrastructure in water because, well, water. Sea cities IRL profit greatly from three acrivities - trade, fishing and oil. That's it. For Civ game system that's not enough so they need to come up with strange arcade solutions like production out of thin air.
I mean, trade and oil significantly improve production capabilities.