Chat Moss is a large area of peat bog that makes up part of the City of Salford, Metropolitan Borough of Wigan and Trafford in Greater Manchester, England. It also makes up part of Metropolitan Borough of St Helens in Merseyside and Warrington in Cheshire. North of the Manchester Ship Canal and River Mersey, 5 miles (8 km) to the west of Manchester, it occupies an area of about 10.6 square miles (27.5 km).
As it might be recognised today, Chat Moss is thought to be about 7,000 years old, but peat development seems to have begun there with the ending of the last ice age, about 10,000 years ago. The depth of peat ranges from 24 to 30 feet (7 to 9 m). A great deal of reclamation work has been carried out, particularly during the 19th century, but a large-scale network of drainage channels is still required to keep the land from reverting to bog. In 1958 workers extracting peat discovered the severed head of what is believed to be a Romano-British Celt, possibly a sacrificial victim, in the eastern part of the bog near Worsley.