A spring-fed river that begins at the bottom of Spring Lake on the Texas State University campus, holds 72 degrees Fahrenheit year-round regardless of air temperature, supports eight threatened and endangered species found nowhere else on Earth, and serves as the primary recreational draw for a city of 67,000 -- all within a 3.8-mile stretch of headwaters that is simultaneously a federally protected habitat and one of the most popular tubing destinations in Texas.
The San Marcos River is not a typical Hill Country river. It does not flood and recede with the seasons the way the Blanco or Pedernales do. It does not depend on rainfall. Its source is the Edwards Aquifer -- a massive underground limestone reservoir that discharges through approximately 200 spring openings at the bottom of Spring Lake, producing a flow that has never gone dry in recorded history. The springs are the second-largest in Texas by volume (after Comal Springs in New Braunfels), historically averaging around 175 cubic feet per second, though flow varies with aquifer levels and regional pumping. The result is a river that is always clear, always 72 degrees, and always flowing. That consistency is what makes it both ecologically irreplaceable and recreationally magnetic -- and managing the tension between those two facts is the central challenge of San Marcos as a city.
The upper 3.8 miles of the San Marcos River -- from Spring Lake through the city to roughly the I-35 crossing -- is designated critical habitat for eight threatened and endangered aquatic species:
1. Fountain darter (Etheostoma fonticola). A small fish found only in the San Marcos and Comal rivers. Depends on aquatic vegetation, particularly Texas wild rice.
2. Texas blind salamander (Eurycea rathbuni). Lives in the subterranean waters of the Edwards Aquifer beneath San Marcos. Eyeless, unpigmented. Never surfaces voluntarily.
3. San Marcos salamander (Eurycea nana). Lives in the spring openings themselves. Visible on glass-bottom boat tours at the Meadows Center.
4. San Marcos gambusia (Gambusia georgei). A small fish that may already be extinct -- not seen since 1983. Listed as endangered, not delisted.
5. Texas wild rice (Zizania texana). Exists only in the San Marcos River. Looks like long grass waving in the current. People mistake it for seaweed and uproot it. Do not touch it.
6. Comal Springs riffle beetle. Tiny aquatic beetle dependent on clean, flowing spring water.
7. Peck's cave amphipod. A crustacean living in spring openings.
8. Comal Springs dryopid beetle. Another aquatic beetle of the spring ecosystem.
This is why the rules exist. The river is not regulated because the city wants to be difficult. It is regulated because the alternative is the extinction of species that have no other home.
Single-Use Beverage Container Ban (effective May 1, 2024). Within city parks and on the river:
- Reusable drink containers only in "No Zones" (the river itself and along the banks). Reusable means metal or thick plastic with a screw-on or unclasp lid.
- Disposable containers (cans, plastic bottles, pouches) are permitted only in designated "Go Zones" -- the picnic-table areas set back from the water.
- One cooler per person, under 30 quarts, in the No Zones. No foam coolers.
- No glass anywhere. No styrofoam anywhere (including foam floats, kickboards, coolers).
- Containers holding five fluid ounces or less are banned park-wide.
- Snacks in original packaging are fine but keep disposable wrappers away from the water.
Rio Vista Park access (summer season, Memorial Day through Labor Day):
- Temporary fencing installed with staffed entry points.
- Park Ambassadors check for banned containers and remind visitors of rules.
- $5 entry fee for non-residents (2025-2026 season; date and amount subject to change -- check sanmarcostx.gov before visiting). San Marcos residents enter free with ID.
- About 70 percent of summer weekend visitors are from out of town. The fee and fencing exist because of the volume.
General river rules:
- No lifeguards anywhere on the river. It is a natural waterway, not a managed attraction.
- Life vests recommended for children and weak swimmers.
- The float does not loop back. You end up downstream of where you started.
- Do not uproot aquatic vegetation (especially Texas wild rice).
- Do not feed or harass wildlife.
- No motorized watercraft in the upper river.
This is the short float -- 45 minutes to one hour, depending on water level and how often you stop. You enter at City Park (off University Drive) and exit at Rio Vista Park (off Cheatham Street). The river is shallow in places (2-3 feet), deeper in pools (6-8 feet), and moves at a walking pace.
Lions Club Tube Rental is the only outfitter within city limits. Located in City Park. Pricing (approximate, 2025-2026 season): $25 per tube with shuttle service, all-day use between 10am and 7pm. Last new tubes issued at 5pm; last shuttle at 6:30pm. San Marcos residents: free for the first 30 minutes, $5 for 30 minutes to one hour, $10 for one to two hours, $15 for three or more hours. If you bring your own tube, shuttle-only service is approximately $15.
If you skip the shuttle, the walk back from Rio Vista to City Park is 10-15 minutes on hot pavement. Bring footwear.
Rio Vista Falls is within this stretch -- three natural limestone drops in sequence. The falls are not large (3-5 feet each) but the depth and debris at the bottom change daily. If you do not want to go over them, exit the river to the left of the falls. There is a portage path. Do not attempt the falls on an inner tube if you cannot swim.
The longer float begins outside city limits and runs through agricultural land to Martindale, approximately 7 miles east of San Marcos. This is a three-to-four-hour float (longer by kayak if you stop frequently). The river is wider, slower, and less crowded than the in-town stretch. There are no falls or rapids.
Two outfitters operate this stretch:
Texas State Tubes -- located just east of San Marcos off the river. Provides tubes, shuttle service, and parking. The float runs approximately 2.5-4 hours depending on water level and stops.
Don's Fish Camp -- located in Martindale. Three-hour float. Tube rental available on-site or by advance online reservation. They bus you upriver and you float back to your vehicle. Also rents cooler tubes and sells ice.
This downstream stretch is Martindale's entire reason for appearing on the map. See the Martindale page for more detail on what is (and is not) there.
Weekdays vs. weekends: The difference is stark. Summer weekends (Memorial Day through Labor Day), the in-town float is crowded -- hundreds of people in the water, lines at Lions Club, Rio Vista packed. Weekdays in the same period are a different river: manageable crowds, no lines, more space. If you have any flexibility, go on a Tuesday or Wednesday.
Shoulder season (March-May, September-October): The water is still 72 degrees. The air is cooler but comfortable. Crowds are minimal. This is when locals float.
Winter (November-February): The water is warmer than the air. Floating is possible but uncommon. The river is essentially empty. Some people swim at the springs year-round -- the 72-degree water feels warm when the air is 45.
The monitoring station for the San Marcos River at San Marcos is USGS 08170500. It measures discharge (flow in cubic feet per second), gauge height, and water temperature. A second station downstream near Martindale is USGS 08171400. Check these before floating if there has been heavy rain upstream -- the Blanco River feeds into the San Marcos system and can cause rapid rises after storms.
Normal base flow from the springs: approximately 100-200 cfs depending on aquifer conditions. When the Blanco is flooding, the combined flow at the downstream gauge can spike dramatically.
The San Marcos River is the reason San Marcos exists. It drew people 12,000 years ago and it draws them now. The difference is that 12,000 years ago, a few dozen people camped at the springs. Today, 67,000 live in the city, 44,000 attend the university, and hundreds of thousands visit annually to float. The river has not gotten bigger. The demands on it have.
The container ban, the fencing, the park ambassadors, the $5 fee, the habitat conservation plan -- none of this is arbitrary. It is the cost of keeping a river alive while letting people use it. The alternative is what happened to other Texas spring systems: pumped dry, polluted, or loved into ecological collapse. San Marcos is trying not to be that story. Whether it succeeds depends on the aquifer, the growth rate, and whether visitors respect the rules or treat them as suggestions.
San Marcos River. Source: San Marcos Springs (Edwards Aquifer), Spring Lake, San Marcos TX. Length: approximately 75 miles to confluence with Guadalupe River. Temperature: 72°F year-round. USGS gauge: 08170500 (at San Marcos), 08171400 (near Martindale).
Planning a trip to the San Marcos River? Ask Dee Dee, the local guide, anything — the crystal-clear springs, the float, the swimming, or where to stay nearby. Ask Dee Dee at sanmarcos.ai →