Officers were called around 2.30pm yesterday (September 18) after a person was seen in the water.
They arrived with paramedics and the fire service but a man was pronounced dead at the scene.
Enquiries are ongoing and a scene was in place into the evening.
A force spokesperson said: “Police were called at 14:28hrs on Thursday, 18 September to London Road, Mitcham following the concern for welfare of a man in the water.
“Officers attended with the London Ambulance Service and the London Fire Brigade. Sadly, a man was pronounced dead at the scene.
“Enquiries are ongoing and a scene remains in place.”
