A man was taken to hospital after falling from Wearmouth Bridge into the river.
Emergency services were called to the scene just before 2.30pm.
A Northumbria Police spokeswoman said: "At 2.24pm police received a report a man had fallen from Wearmouth Bridge in Sunderland.
"Officers are at the scene, working together with the fire and rescue service.
"Anyone who was in the area at the time, or anyone who has any information that could help police, have been asked to contact officers on 101 quoting reference 0557 200417."
The man was taken to hospital however, his condition is not yet known.
Paul Nicholson, senior helmsman at Sunderland RNLI, said: "Our Atlantic 85 lifeboat was launched to the scene after we got the call.
"At the scene there was a female student who had seen what was going on and she climbed down one of the ladders at the riverside to get hold of the guy.
"She held onto him until the emergency services arrived.
"The fire brigade arrived and one of the officers swapped with the student, then our lifeboat arrived and transferred the man on to the lifeboat where first aid commenced."
The man was then taken to Sunderland Royal Hospital by ambulance.
Mr Nicholson praised the quick-thinking actions of the student.
"She did an excellent job in assisting the emergency services with the rescue," he added.
"We would recommend that people be careful when doing this when they don't have the correct equipment, but she didn't put herself in any immediate danger."