Arroyo Napostá is located in the region of Bahía Blanca, Buenos Aires Province, Argentina It is a stream whose watershed is in Sierra de la Ventana, about 120 kilometres (75 mi) northeast to Bahía Blanca. It was essential during the early history of the city of Bahia Blanca as a source of water and also as a natural defense against aborigine. Later on it was useful as a water supply for agriculture.