Police said 28 people were collecting sand in 10 trucks from the river bed beside Chormundi village under Beliabera police station.
Suddenly 2.85 lakh cusec water was released from Galudi dam and the nearly dry river bed got flooded.
Those people who were working on a relatively higher zone in the river bed suddenly found that it had become an island with water flowing surrounding the area, police said.
After being informed, the police and Gopiballabhpur II Block Development Officer Kaushik Ghosh reached the spot and those sand miners were rescued by boat.
The 28 people included truck drivers and they came from Kolkata, Howrah and North and South 24 Parganas districts, police said.