Water-quality summary of the San Marcos Springs Riverine System, San Marcos, Texas, July-August 1994

San Marcos Springs is the second largest spring in Texas and is the headwaters for the San Marcos River in San Marcos. Spring Lake (fig. 1) was built in 1848 at the site of a marsh formed by the springs to provide hydropower to a mill. The San Marcos River originates from the 15-acre lake and flows approximately 4 river miles (mi) south to its confluence with the Blanco River. The mean annual flow of the San Marcos River is about 170 cubic feet per second (ft³/s).