Josef mentions that in Germany it was against the law for people to swim. Most of Josef's people appear to be German Lutherans, which is why they have a lot of strict religious customs, like no carrying weapons and no killing, even in self defense. However the law against swimming was not for religious reasons, it was a public health issue. Most of the rivers in Europe at the time were badly polluted, swimming in them could expose a person to a number of highly contagious diseases, as such a number of areas had laws against swimming in rivers.
According to the meeting between Shea, Thomas, James, and Wade : With respect to the ferrying of people, cattle and wagons over a river crossing; if cattle were to trample the banks, it would make it difficult for wagons (stuck and create a traffic jam) and people to cross; the correct sequence would be people, wagons and then cattle "Wagon train" should fatten up before their trek across the Oregon Trail If a cow were to be butchered without the expert hand of experienced chef, most of the meat would go to waste.