San Marcos River level at San Marcos
Texas · Tubing & floating
Measured at USGS 08170500 — San Marcos Rv at San Marcos, TX · NWS forecast point SRUT2
Reading taken · as of 43 min ago
Running thin — a slow, scrapey float
At 91 CFS, this gauge is in the lowest quarter of the 31 years USGS has recorded for this date (1995–2026), at 63% of the 145 CFS median.
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Flow history at San Marcos
Daily values from USGS 08170500, updated every 15 to 60 minutes; NWS forecast for SRUT2 reissued through the day. Provisional.
Highest crests on record at San Marcos
2 on record
| Stage | Flow | Date |
|---|---|---|
| 21.29 ft | 21,500 CFS | Oct 17, 1998 |
| 10.77 ft | 2,470 CFS | Jul 8, 2002 |
Crests published by the National Weather Service.
About San Marcos River at San Marcos
The daily record here spans 111 years but contains only 13,868 values. The series opens on 1 July 1915 and runs to the present, yet that is about thirty-eight years of data spread across a century, so the record is not continuous and the published daily statistics window covers only 1995 to 2026.
That matters for reading the extremes. The record low of 46 CFS, from 15 August 1956, comes from an earlier era of the record entirely, decades before the statistics this page compares against. The record high of 6,200 CFS, on 17 October 1998, is inside the modern window, and the instantaneous peak that day reached 21,500 CFS at 21.29 feet, more than four times the next largest peak on file. Day to day the river is remarkably flat: monthly medians from 147 CFS in September to 179 in June, a twenty percent spread on a 48.9 square mile spring-fed drainage.
San Marcos River at San Marcos — common questions
6 questions
Why is the record low so much older than the rest of the record?
Because the daily series is discontinuous. USGS has values here going back to July 1915, but only about 13,868 of them across those 111 years, and the published statistics window is 1995 to 2026. The 46 CFS low of August 1956 sits in a gap-filled older portion of the record, so it is real but it is not drawn from the same period as the medians on this page.
How unusual was October 1998?
Extremely, on this station's record. The annual peak of 21,500 CFS at 21.29 feet is the largest of the thirty-one peaks on file, and the second largest is 5,100 CFS at 14.4 feet from May 2015. Only two crests appear on the NWS list at all: 21.29 feet in October 1998 and 10.77 feet in July 2002.
Does the Martindale gauge downstream tell me anything?
Yes, and it is the closest peer in this batch. The San Marcos at Martindale is 6.8 miles away on the same river, and over 5,530 shared days since May 2011 the two correlate at 0.859, with this gauge running at a median of about 0.87 times the Martindale reading. Same river, same springs, with a little more drainage picked up between the two.
Does rain upstream change San Marcos River at San Marcos quickly?
Yes. It is free-flowing, so rain upstream moves it directly. Several feet in a few hours is normal after a heavy storm.
Is San Marcos River at San Marcos high or low for this time of year?
The USGS median flow for late September here is 145 CFS, from 31 years of record (1995–2026). Today sits in the lowest quarter of those years, at 63% of the median. The comparison is what makes the raw number mean anything: the same reading is a drought on one river and a flood on another.
How often does this reading update?
USGS transmits from gauge 08170500 every 15 to 60 minutes, and the National Weather Service reissues the flood forecast for SRUT2 a few times a day — more often when the river is rising. This page refreshes from both when you open it. The timestamp is in the gauge's local time.