Risley Moss is an area of peat bog situated near Birchwood in Warrington, England. It is a Site of Special Scientific Interest and a Local Nature Reserve. It covers an area of 210.5 acres and is one of the last remaining fragments of the raised bogs that once covered large areas of South Lancashire and North Cheshire. Natural depressions in the glacial drift left by the ice sheets which covered the Cheshire–Shropshire plain during the last ice age, 10,000–15,000 years ago, filled with water, forming the meres and mosses characteristic of the area today. In some cases, like Risley Moss, peat accumulation filled the depression, allowing colonisation by bog mosses such as the Sphagnum varieties, thus giving rise to the name "moss".
Risley Moss is one of only two mosses in Cheshire where the water level has been deliberately raised in an attempt to encourage the regeneration of an active bog surface. The long-term restoration project to re-wet the moss began in 1978 and was completed in 2002. This scheme was undertaken to create a series of scrapes and bunds to retain water and recreate the perfect conditions for bog flora such as cotton grass and sphagnum mosses to re-colonise the bogs.
It was the former site of a large Royal Ordnance Factory. Today, it is managed by Cheshire County Council as a country park and an educational nature reserve. It was designated a Site of Special Scientific Interest in 1986. Risley Moss, together with Astley and Bedford Mosses and Holcroft Moss, is also a European Union designated Special Area of Conservation, known as Manchester Mosses.