The Brahmaputra isn't actually India's only "male" river. It earned its masculine title by being a fiercely destructive force of nature unleashed by a mountain-cleaving battle axe.
The Indus (Sindhu), Son, and Damodar rivers are also traditionally classified as masculine in Hindu mythology and Sanskrit grammar.
Rivers in India are typically personified as feminine goddesses (Nadi) because they are seen as nurturing, life-giving mothers who sustain agriculture and settlements along their banks, such as the Ganga, Yamuna, or Godavari. Rivers categorized as male (Nada) earn that designation through a combination of mythological lore and harsh geographical reality.
The Brahmaputra’s name translates directly from Sanskrit as "Son of Brahma." According to the Kalika Purana, the creator deity Brahma had a child with Amogha, the wife of the sage Shantanu. The child took the form of water and was placed in a valley between four mountains to contain its immense energy. It remained trapped there until the warrior sage Parashurama used that legendary axe to cleave the mountains apart, releasing the water down into the plains of Assam to wash away his sins.
Geography reinforced this masculine persona. The Brahmaputra does not behave like a gentle, nurturing mother. It is one of the world's most turbulent waterways, carrying a colossal volume of water and a heavy sediment load from the high Himalayas. Its course is highly dynamic and braided, prone to catastrophic flooding and severe bank erosion during the monsoon season. This fierce, unpredictable, and destructive force is culturally associated with masculine energy, contrasting sharply with the steady, life-giving archetype of India’s female rivers.