Drifting down the San Marcos River in a tube is very pleasant. Because the San Marcos River is spring-fed, it tends to be one of the few rivers that is runnable during periods of drought. The river is clean and cool, most of the scenery is natural, most of the other tubers are pleasant, the waterfall is fun and the ability to enjoy a beverage during the drift makes it even better . A small fee is required. San Marcos River Toobing. To avoid the parking hassles at Westerfield Crossing, many paddlers use San Marcos River Retreat (a private campground at river left) as an alternate takeout for this run. It generally has more rapids than the upper stretch, although none of the rapids are difficult. There are plenty of wide easy stretches to the river, and the clarity is great. It's much like the Comal, but less crowded, and less fuss. The San Marcos River is spring fed starting in downtown San Marcos, TX. San Marcos River: Tubing & Rapids - See 391 traveler reviews, 121 candid photos, and great deals for San Marcos, TX, at Tripadvisor. There is a large stretch of flat water above Martindale Dam. Next set of ripples, about a easy class II, sets up by a easy left turn, a 1-2 foot drop and a… Note also that San Marcos River Retreat does not allow alcohol on its premises. The river is a constant 72 degrees. If you've never toobed the San Marcos river, you should. This section is a great run for whitewater beginners. Further down a river right portage is needed to go around an island, and then you weave around through a good flat-water paddle. Spring fed, this short gem was made for floating.