The Twelve Mile Swamp Conservation Area is composed of a series of large swamps, planted pine forest and several small cypress domes. Together, the swamps of this conservation area form the headwaters of six major tributary systems. Three of these tributaries, Turnbull Creek, Mill Creek and Sampson Creek, discharge into the St. Johns River. Two others, Moultrie Creek and Red House Branch, discharge into the Matanzas River, while Stokes Creek discharges into the Tolomato River. The conservation area protects the water quality and quantity of these creek systems and benefits the groundwater and water supply for this area of St. Johns County, providing a buffer for a wellfield that supplies drinking water in the county.