When it is necessary to create the material universes, Viṣṇu expands Himself as Mahā-Viṣṇu. Mahā-Viṣṇu lies down in the Causal Ocean and breathes all the universes from His nostrils. Thus from Mahā-Viṣṇu and the Causal Ocean spring all the universes, and all these universes, including ours, float in the Causal Ocean. In this regard there is the story of Vāmana, who, when He took three steps, stuck His foot through the covering of this universe. Water from the Causal Ocean flowed through the hole that His foot made, and it is said that that water became the river Ganges. Therefore the Ganges is accepted as the most sacred water of Viṣṇu and is worshiped by all Hindus, from the Himalayas down to the Bay of Bengal.
Mahā-Viṣṇu is actually an expansion of Balarāma, who is Kṛṣṇa's first expansion and, in the Vṛndāvana pastimes, His brother. In the mahā-mantra—Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare—the word "Rāma" refers to Balarāma. Since Lord Nityānanda is Balarāma, "Rāma" also refers to Lord Nityānanda. Thus Hare Kṛṣṇa, Hare Rāma addresses not only Kṛṣṇa and Balarāma but Lord Caitanya and Lord Nityānanda as well.