Texas · Castell, TX
Llano River float season
Gauge 08151500 on the Castell to Llano through the granite islands. Wide granite-country water dotted with pink boulders and islands, a favorite overnight paddle when spring rains bring it up.
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 Llano River. Provisional data — subject to revision.
The year on this river
In a typical year at the Castell gauge, the Llano River runs fullest Mar–May and leanest Jul–Sep. Where today's reading falls inside that rhythm matters more than the raw number — the same flow that feels thin in spring can be the summer norm. Half of all past May days at this gauge ran above 178 CFS; the August median is 73 CFS.
| Month | Typical flow (CFS) | Relative volume |
|---|---|---|
| January | 156 | |
| February | 165 | |
| March | 162 | |
| April | 155 | |
| May | 178 | |
| June | 140 | |
| July | 87 | |
| August | 73 | |
| September | 112 | |
| October | 136 | |
| November | 152 | |
| December | 158 |
Record context
This gauge has measured daily flow since 1939 — 87 years of record. The largest daily average ever logged here was 166,000 CFS, in October 2019. 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 Llano River usually at its fullest?
At the Castell gauge, the fullest stretch of a typical year is Mar–May, with the single highest monthly median in May (about 178 CFS). The leanest months are usually Jul–Sep.
What is a typical summer flow on the Llano River?
The July median at this gauge is about 87 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 Llano 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 87 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 08151500 (Llano Rv at Llano, TX), chosen because it best represents the Castell to Llano through the granite islands. Daily records here reach back to 1939.
Data: USGS gauge 08151500, approved daily records 1939–2026, retrieved 2026-08-07. Live readings are provisional and subject to revision. U.S. Geological Survey data is public domain.