Texas · San Marcos, TX
San Marcos River float season
Gauge 08170500 on the City Park through Rio Vista Falls to Cape's Dam in San Marcos. Crystal spring water at a near-constant 72 degrees, with Rio Vista's chutes turning a city-park float into a rite of passage for students and townies alike.
Right now at this gauge
loading CFS
Checking the live gauge…
Well above typical for this date
Live reading from the USGS gauge page for San Marcos River. Provisional data — subject to revision.
The year on this river
In a typical year at the San Marcos gauge, the San Marcos River runs fullest May–Jul and leanest Aug–Oct. The swing is small by river standards — flows hold fairly steady through the seasons, which usually points to springs or dam releases doing the work. Half of all past June days at this gauge ran above 179 CFS; the September median is 147 CFS.
| Month | Typical flow (CFS) | Relative volume |
|---|---|---|
| January | 161 | |
| February | 157 | |
| March | 159 | |
| April | 164 | |
| May | 174 | |
| June | 179 | |
| July | 172 | |
| August | 153 | |
| September | 147 | |
| October | 150 | |
| November | 175 | |
| December | 163 |
Record context
This gauge has measured daily flow since 1995 — 31 years of record. The largest daily average ever logged here was 6,200 CFS, in October 1999. Rivers do that sometimes; it's why the safety panel above isn't decoration.
Planning dates? The trip-window checker shows what flows have historically looked like on any week you pick for this river, or see what a CFS actually looks like.
More Texas float rivers
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Blanco River
Wimberley through the cypress-lined bends toward Five Mile Dam near Kyle
Fullest: Mar–May
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Brazos River
Below Morris Sheppard Dam at Possum Kingdom down to the Highway 180 bridge
Fullest: Jun–Aug
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Colorado River
El Camino Real paddling trail from Bastrop toward Smithville
Fullest: May–Jul
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Comal River
Prince Solms Park through the Tube Chute to the Guadalupe confluence
Fullest: Jan–Mar
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Frio River
Garner State Park through the Concan crossings
Fullest: Mar–May
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Guadalupe River
Canyon Dam tailrace from Sattler through the Horseshoe Loop toward New Braunfels
Fullest: Apr–Jun
Common questions
When is the San Marcos River usually at its fullest?
At the San Marcos gauge, the fullest stretch of a typical year is May–Jul, with the single highest monthly median in June (about 179 CFS). The leanest months are usually Aug–Oct. This river holds unusually steady across the year, so the swing between those extremes is small.
What is a typical summer flow on the San Marcos River?
The July median at this gauge is about 172 CFS — half of past Julys ran higher, half lower. Late summer is this river's lean season, so expect readings to drift down as the season goes on.
Is the San Marcos River safe to float right now?
No flow number can answer that, and this site never labels a river safe. What the data can tell you is how today's reading compares with 31 years of this date's history — well above typical means pushier, colder, faster water. Pair that context with a PFD, a look at the river from the bank, and a call to a local outfitter before you commit.
Which USGS gauge does this page use?
USGS gauge 08170500 (San Marcos Rv at San Marcos, TX), chosen because it best represents the City Park through Rio Vista Falls to Cape's Dam in San Marcos. Daily records here reach back to 1995.
Data: USGS gauge 08170500, approved daily records 1995–2026, retrieved 2026-08-07. Live readings are provisional and subject to revision. U.S. Geological Survey data is public domain.