Saline waters reach the surface in a large area of the SE. Copper River Lowland and are estimated to add more than 200 tons of chloride per day to the Copper River. Most saline springs in the area are similar in composition to connate waters of the Na-Ca-Cl type, and are accompanied by gases composed mainly of methane and N. In the E. part of the saline area 3 springs discharge Na-Cl-HCO 3 type water that is thought to be basically water of the Na-Ca-Cl type admixed with water rich in HCO 3 , B, and SO 4 . These springs discharge CO 2 gas. It is postulated that the Na-Cl-HCO 3 waters are the result of mixing at depth of waters of the Na-Ca-Cl type with fluids of volcanic, metamorphic, or other origin. Chemical data slightly favor a metamorphic origin for the admixing fluids. The saline water is thought probably to originate in Upper Cretaceous or older marine sedimentary rocks which are inferred to underlie the southern part of the Copper River Lowland.