The 13-year-old was removed from the River Kelvin in Glasgow shortly after 8pm.
He was taken to the city's Western Infirmary by ambulance where he later died.
A Strathclyde police spokesman said it was unclear how the boy came to be in the water.
Police, firefighters and ambulance services all attended the scene close to the West of Scotland Science Park.
The boy will not be named by police until all his family have been told of his death.