The practice of dropping bodies into the swamps as a burial ritual was actually a relatively new thing to those refugees from the southern lowlands. They had the firm fertile clay soil that didn’t shift easily, and so buried their dead there.
The northern highlands have loam. In many places, it’s packed down so water saturating it will still retain a certain firmness to walk across. But in quite a few places, it’s loose, meaning there’s a fair bit of air pockets in it.
The northern clans tried many times to bury their dead, but every spring and fall rainy seasons, they had trouble with unexpected visitors when the water filled these air pockets and pushed bodies to the surface. It’s a very startling thing to be visiting a dead ancestor only to see them go whizzing passed you on torrential run-off, especially since Preussans are known to honor their dead. You could see entire families of people running after their vagrant deceased. Such was such a problem that for almost two hundred years, a new job known as ‘Waterman’ was devised for the sole purpose of paying someone to watch out for bodies blooping to the surface during the rainy seasons.
Preussans are very much about giving back physical form to the earth. The earth is not only their means of sustenance, but they also have a firm belief that they were born from it as a species. Dust to dust, and all that. So the shock and upset that the earth didn’t want to take them back made them devise a different burial method that could fulfill this. Only part of this decision was because chasing Grandpa down the hills on a macabre Slip-n-Slide was more than a little distressing. Using a different belief of theirs in which veins spread across Preussas originating from the central swampland gave them their idea to start sinking the dead instead. There, they could liquify in peace and in turn, sweep through the land via the Veins.
Watermen had a new purpose after this, catching dead bodies as they bobbed to the surface during the rainy seasons to be rewrapped in a shroud and tied with a gold cord before being hoisted to the swamps to be dropped in. By the time the surviving southern clans came to merge with the untouched northern clans, the practice had been established and was passed on to those newcomers.
While the job of Waterman is no longer available as those bodies in question have been moved, every so often someone’s bones still wheedle their way to the surface after all this time and end up on someone’s front doorstep. Much to the morbid amusement chagrin of the unlucky recipient.