Is part of the Coxs River Water Supply Scheme and is located 8km south west of Lithgow. This concrete faced, rock filled dam with a height of 46m was completed in 1982 and upgraded in 1992. The northern headwaters of the dam are within the Marrangaroo National Park. Named after John Frederick Lyell (1862-1913), who established his property fronting the Coxs River in 1893.