Northumbria Police said that Aras Rudzianskas, 13, of Newcastle, died in hospital on Tuesday.
David Radut, 14, of Newcastle, died at the scene near the Ovingham Bridge on Saturday.
Chief Superintendent Sam Rennison of Northumbria Police said: “Our heartfelt condolences go out to the families of both lads, and we will continue to provide any assistance we can at this difficult time.
“Since Saturday, our and the wider community’s sympathies have been with the relatives and friends of those affected.
“We would ask that the public continue to respect the privacy of the families both online and in the community.”
