A police investigation has been launched after a man's body was found in a car submerged in a Southland river.

The dead man recovered from Mataura River was Te Iwiroa Manakura Te Hapuka Smith, 44, of Curio Bay.

Detective Grant Johnstone, of Invercargill, said police national dive squad members from Wellington found Mr Smith in a car submerged in the river, near Fortrose.

Police were called to Holz Rd on Monday after a report a car had entered the river about 5.30am on Monday.

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The dive squad was called after police, Marine Search and Rescue and Coastguard were unable to confirm if anyone was in the car.

The squad members entered the river about noon today and confirmed Mr Smith was alone in the vehicle.

A car was removed from the river today.Police have launched a serious crash investigation to determine how the car entered the river and were assisting Mr Smith's family.