Bhagirathaprayatnam King Sagara, the great-grandfather of Bhagiratha, once performed the ashvamedha sacrifice, but the sacrificial horse was stolen by Indra. The deity had the animal sequestered in Patala, where Sage Kapila was performing a penance. The 60,000 sons of Sagara discovered the horse in Patala, whereupon they disturbed Kapila with their hoarse noises. Infuriated, the 60,000 sons of Sagara were reduced to ash by the fiery eyes of the sage. The responsibility of performing the funeral rites of these sons passed down from generation to generation, until it was acquired by Bhagiratha, who upon his ascension to the throne of Ayodhya, went to practice austerities in the Himalayas, to invoke the goddess Ganga. Ganga told Bhagiratha that were she to descend from Svarga to the earth, the force of her fall would be difficult to sustain. She asked him to obtain the favour of the matted-haired, blue-throated deity Shiva, as no one except him would be able to sustain her. Heeding her words, the king then performed a penance that lasted for a millennium for Shiva at Kailasa, and sought his cooperation in allowing Ganga to flow through his hair. Shiva granted him the boon, and stood in position, even as the torrent of Ganga's stream rushed upon his hair. Ganga flowed along the matted hair of Shiva for a thousand years. Bhagiratha performed another penance to please Shiva, until the deity shook his hair and allowed a single drop to descend upon the Indo-Gangetic plain, which became the Ganges. For Bhagiratha, the river flowed along the plain to Patala, and performed the funeral rites of Sagara’s sons.^[3] This episode is referred to as Bhagīrathaprayatnam, literally meaning, "Bhagiratha's labour".

        To commemorate his efforts, the head stream of the river is called Bhagirathi by locals, till it meets the Alaknanda river at Devprayag. The mythical pātāla where the sage Kapila meditated is identified with the Sāgar Island, at the confluence of the Bhagirathi stream of the Ganges (flowing by Kolkata and revered as Ganga) and the Bay of Bengal. The sea (sam-udra) is called Sāgara in honour of Bhagiratha's ancestor the King Sagara. Kapila's ashrama is located at Sagar Island and hosts the annual Ganga Sagar Mela and bathing rituals on Makara Sankranti day every year.

       While flowing towards Patala, the Ganga flooded the ashrama of Sage Jahnu. To punish the haughtiness of the goddess, the sage swallowed the river. It was with the insistent entreaties of Bhagiratha that the sage consented to push the river out through his ear, which offered the goddess the epithet Jahnavi.