It depends who you believe really. Approximately 20 urns were filled with ashes of the assassinated Ghandi, and the urns were transported throughout the country to comply with Gandhi's wish that his remains be immersed in the rivers of the country.
According to his wish, the majority of his ashes were immersed in all the major rivers of the world such as Ganges, The Nile, Volga, Thames, etc. Also, a small portion was sent to Paramahansa Yogananda from Dr. V.M. Nawle, (a publisher and journalist from Poona, India) encased in a brass & silver coffer. The ashes were then enshrined at the Mahatma Gandhi World Peace Memorial in the Self-Realization Fellowship Lake Shrine within a thousand-year-old stone sarcophagus from China.
Another story emerges that one urn was transferred to Cuttack, the capital of the Indian state of Orissa, where it was apparently placed in the state bank vaults until January 1997 when, nearly 50 years after his assassination, the ashes of Mahatma Gandhi were spread in the Ganges river during a ceremony honouring his memory in Allahabad, India.
So in simple terms, it was what he had requested. Symbolically, to assure quick salvation of the soul, the Hindus believe that one must seek to breath one's last lying on the bank of a sacred river (Hinduism considers any river a holy river) with a flurry of prayer emanating from his mouth. Ganges, is the holiest of them all, considered so holy that every Hindu wishes to be anointed by the Ganges river's water at his death's door.