I'm not quite sure what your premise is: whether giving a river personhood is novel or not novel in Anglo law. But FWIW granting inanimate things a legal personality (with rights and even duties!) has a long history not only in English Common Law but also the Western legal tradition back to the Ancient Greeks.[1] I doubt the practice is confined to the Western legal tradition as it has immense practical utility and is an obvious hack to most any legal system.

[1] See, e.g., Lawrence B. Solum, Legal Personhood for Artificial Intelligences, 70 North Carolina Law Review 1231, 1239 (1992) (https://scholarship.law.unc.edu/cgi/viewcontent.cgi?article=...)