Purokayastha also said the accident was partly caused by a transport bottleneck.
The ferry service to the island had been temporarily suspended during low tide, resulting in a large crowd building up on the mainland side.
When the service resumed, the first vessel to dock was swamped by pilgrims.
Ritual bathing festivals were held along the length of the Ganges on Thursday as part of harvest festival celebrations across the country.
This year, the ceremonies coincided with the Kumbh Mela festival taking place in the northern city of Haridwar, where millions have gathered to cleanse themselves in the Ganges.
Several million people are set to take part in the Kumbh Mela, the world's biggest religious gathering which takes place every three years and runs for three months.