The Blanco River headwaters are springs in northwestern Kendall County, near the Gillespie County line. Flowing east southeast for about 87 miles, the Blanco River passes through Kendall, Blanco and Hays Counties to its mouth at the confluence of the San Marcos River just southeast of the Town of San Marcos. The name of the river derives from members of the Aguayo Spanish Expedition in 1721, after they encountered the white limestone in the streambed and along the riverbanks - Rio BLanco (White River).Blanco River is not frequently navigable. It flows best at or near flood stage, and quickly dissipates back to its placid self. Right after a good rainstorm is the best time to catch the Blanco, and for that reason great care should be taken when canoeing or kayaking the Blanco.
The water quality in the Blanco River is generally considered very good, though the river is usually far too low to paddle. The Blanco River usually has an adequate flow for paddle trips during and shortly after a flood, then the flow quickly returns to minimal after runoff water has been drained into the river. Flow levels are subject to extreme fluctuations that can occur on a moment's notice, especially if rains fall anywhere within the drainage basin for the river, so beware of the potential for flash flooding.