Erymanthos was the Potamoi of the same name as his river (as well as a nearby mountain). He was not an overwhelmingly vital god. His river was one of several tributaries which flowed into the Alpheios. It did so near the Eleian border. Its joined at the Eleian border after having flown southernly from the Erymanthos and Pholoe mountains, down past a town called Psophis where it finally joined the Alpheios River.
Okeanos & Tethys