From the Game's Setting:
Aquaero is a world brimming with mystery and adventure. The planet's surface is nothing but water as far as the eye can see and always has been since time immemorial. But man does not live on the seas. Instead he lives in the many massive cities floating in the skies. All told there are several hundred such cities in Aquaero, each typically several hundred miles apart and at least a mile off the surface. As such, travel in Aquaero takes place almost exclusively by air. Gyrocopters taxi people about the cities. Planes of all sizes and shapes run goods to and from the various ports of various cities, and the wealthy take cruises in zeppelins and dirigibles. There are a few boats, but not many. Sea travel is slower, less efficient (unless those aboard are using sails), and just as dangerous. The waves can become violent, as can the creatures of the deep. All of this is to say nothing of the hassle of transferring goods from boat to plane. Still, the threat of running out of fuel and crashing into the seas is a very real danger, especially considering the ever-shifting nature of cities. As such, almost every aircraft in existence comes equipped with pontoons or other gear for a water landing. It's only practical.
Life on Aquaero, or at least human life, lives in the Cities, enormous masses of power and steel sometimes as much as ten miles across suspended in air, held aloft by technology they cannot pretend to understand, a legacy left to them millennia ago by the ancient and enigmatic Engineers. No record remains of who built the cities or how the machinery works. People only know they must keep the generators running at all times or the city loses power. When they lose power, the turbines stop, and an entire civilization crashes to their doom in the icy waters below. These generators run on a rare and precious fuel called trozine gas, which can only be found at the Platforms, refineries resting atop the ocean's surface which gather the crude substance from somewhere within the watery depths and refine it into trozine, after which it is stored in large canisters free for the taking. The entire process, as far as anyone can tell, is automated, and a volunteer police force sprouted up around most Platforms to ensure that no one city monopolizes the trozine. That isn't to say there aren't those who would love to have a trozine refinery all to themselves...