The company announced earlier this year it would carry out a survey for oil deposits below the Brahmaputra running through Assam, a state rich in oil reserves.

But local people said the seismic surveys which would form part of the exploration would hurt marine life and speed up soil erosion. If oil is found, drilling could have even more adverse consequences, they say.

"Our survival is at stake and we will not allow OIL to carry out the survey even if it means death," Chandra Kamal Dutta, a local school teacher, told Reuters.

He is lives in Rohmoria, a village 500 km (310 miles) east of Assam's main city Guwahati, that comes under the OIL survey and where most people grow paddy or fish to survive.

The six-month-long survey, which is expected to begin sometime this month, would involve underwater explosions and firing air gun shots into the riverbed to obtain seismic data.

"The loud bursts disturb, injure and kill aquatic life as has been recorded during such surveys in other parts of the world," Bibhab Kumar Talukdar, a local conservationist, said.

"We anticipate similar effects in the Brahmaputra which cannot be allowed."

The river home to the endangered Gangetic dolphin and other marine life originates in Tibet, flows through Assam and Bangladesh before ending its journey into the Bay of Bengal.

Residents of the area said the seismic survey would accelerate soil erosion along the river bank.

"Once oil exploration takes place in the river, there will be more pollution, dislocation of people living on the banks and destruction of paddy fields will be unimaginable," Talukdar said.

The Brahmaputra, which is also known for its ferocious flooding each monsoon, has already eroded huge chunks of land along its 750-km (466-mile) stretch in Assam and experts say vital parts of farmland would go underwater eventually.

Officials of Oil India, which supplies crude oil and natural gas to four oil refineries of eastern India refused to comment on the exploration controversy.

India's economy has been growing at an average eight percent over the past three years and the country is hungry for more energy, leading to state oil and gas firms stepping up exploration efforts in new areas.

A local geologist said the survey itself would have no impact on marine life because it had adapted to the already high seismic activity in the region which experiences an average of 60 mild tremors every month.

"The magnitude of the sounds made by the air guns will be less than 3 on the Richter scale," geologist Sushil Goswami from the Dibrugarh University in eastern Assam, said.