The emergency services were called to a river in Huntingdon due to concerns for a person.
Police, fire and ambulance crews were in Hartford Road this afternoon after a person was seen entering the water, but not leaving.
A Cambridgeshire Fire and Rescue Service spokesperson said more than 20 firefighters were at the scene with people searching in the water.
Fire crews from Cambridge, Huntingdon and Papworth were called to the river at 1.07pm.
Cambridgeshire police said this afternoon no person was found and that officers have left the scene.