Piriawis
In Mandaean cosmology, Piriawis, also known as the Yardena Rabba, is the sacred life-giving river of the World of Light. It is the heavenly counterpart of rivers on Earth, which are considered by Mandaeans to be manifestations of the heavenly Piriawis.
Shilmai and Nidbai are the two guardian uthras watching over Piriawis.
Qulasta prayers 13 and 17 mention Piriawis-Ziwa and Piriafil-Malaka together as uthras.