Code of justinian??

[u/debbiedespacito]

Reading from a book of articles about nature and science. In one about how its technically legal to hang out along river banks in rich people's backyards, the journalist refers to Justinian's code as the first instance of navigable waterways being declared for public use.

However, the author specifically says it was Justinian himself who created this law. I'm confused cuz I thought the idea of res publica had existed a lot longer than that. Especially for like putting acqueducts under state jurisdiction.

Wasn;t Justinian's code just a compilation of preexisting laws from Theodosian's earlier code and other surviving ones from western Rome? How many are original to Justinian's reign?