Rostherne Mere is a natural lake in Cheshire, England. It is the largest of the Cheshire meres with an area of and a maximum depth of . It lies north of Rostherne village and south of the M56 motorway. Because of its importance for wildlife, the lake, together with neighbouring areas of woodland and pasture, has been declared a national nature reserve, a Ramsar site and a Site of Special Scientific Interest covering .