Saraswati Devi’s worship can be traced back to the early Vedic era in India (ca.1500 BCE), when she was honored in the form of a sacred river of the same name. Long ago, the Vedic sages performed their rituals on Her banks. Hymns in the Rig Veda extol Her might, as Her waters could break the backs of mountains (1). The river itself may be long gone, and the facts of its existence have become the source of much controversy,* but Saraswati remains.
(1.) Rig Veda. Book 6, Hymn 61
*Yes, it’s Wikipedia, but it’s a good overview of the scholarly debates on the subject. So bite me.