Officers were called to Rawnsley Avenue just after 2pm yesterday by members of the public.
No arrests have been made and enquiries are ongoing with formal identification due to take place.
Met Police statement:
At 14:18hrs on Tuesday, 21 May, police were called to Rawnsley Avenue, Mitcham after human remains were found in a river by members of the public.
Officers attended and have set up a crime scene, the road will remain shut until the scene is closed.
Enquiries are on-going into the circumstances and we await formal identification of the remains.
At this early stage, we have not made any arrests.