2. San Marcos City Park to Westerfield Crossing (5.5 miles)

Although Rio Vista Whitewater Park is the primary attraction for whitewater paddlers on the Upper San Marcos, the rest of the run makes for a very scenic float trip, as the crystal-clear 72-degree spring water meanders through cypress trees and past farms.  Above the confluence with the Blanco, the San Marcos is entirely spring-fed (except during runoff events) and maintains its temperature year-round, which makes it a good paddling destination during the winter.  The lush area between Rio Vista Whitewater Park and Thompson's Island is home to some endangered species. There is a lot of flat water on this run, courtesy of the twelve-foot-tall Cummings Dam (below the confluence with the Blanco.)  Apart from Rio Vista Whitewater Park, the rest of the rapids on the run are small and unconsequential, but because the river is mostly spring-fed, it tends to be one of the few rivers that is runnable during periods of drought.  The river is generally runnable down to 100-120 cfs, but some rapids will get scrapey below 200 cfs. Distances and gradient measured using GIS tools in 2015. A note about Spring Lake Dam: Just upstream of the City Park put-in is an artificial waterfall next to the Saltgrass Steakhouse (formerly Joe's Crab Shack.)  This feature is created by a dam that raises the level of the lake around San Marcos Springs (Spring Lake.)  This lake was formerly the site of Aquarena Springs, an amusement park, and now serves as an environmental research center for Texas State University.  Running Spring Lake Dam is illegal.