CCTV investigations in London Road, Kingston found a mound of fat the size of a bus had reduced the 70 x 48cm sewer to just 5% of its normal capacity.
Thames Water has begun repairs to 20 metres of the damaged pipe and work is expected to take up to six weeks to complete.
More top news
Fourteen police officers were injured in protests over death of Edir Da Costa, the Met has confirmed.
A full list of buildings that have failed fire safety checks in London has been confirmed following the tragedy of the Grenfell Tower fire.
One of the youngest victims of the Grenfell Tower tragedy choked to death on fumes from the fire, an inquest heard.