The Kumbh Mela is celebrated at four sacred river banks in India: Haridwar (Ganges), Prayagraj (confluence of Ganges, Yamuna, Saraswati), Nashik (Godavari), and Ujjain (Shipra). Since this question specifies Haridwar, the correct answer is the Ganges river, which is the most sacred river in Hinduism.