Officers were called to reports of a female in the water at Boulter's Lock in Maidenhead at 10:15 GMT.
A force spokesman said fire crews and the ambulance service attended but the woman, who was in her 50s, was pronounced dead at the scene.
Her death is being treated as unexplained and next of kin have been informed.
A woman's body has been pulled from the River Thames in Berkshire.