The moss 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, 10–15,000 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.
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 & Bedford Mosses and Holcroft Moss, is also a European Union designated Special Area of Conservation, known as Manchester Mosses.
Tours across the flats and nature reserve are available from the main information centre and are undertaken by local rangers.