Pool season · Texas
San Marcos Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
San Marcos's whole pool calendar, condensed: when the water warms, when it cools, and where today falls between those edges. Use the opening guide and closing guide for the step-by-step work; keep this page for the dates.
San Marcos, TX — 189 swim days a yearEach dot on the bar is one week of San Marcos's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (February 22–March 15), solid teal is swim season, and hollow amber is the closing window ending November 21. The black marker is today — its position against the colors is the entire executive summary.
The San Marcos pool calendar
Opening — target March 1
Target March 1; the practical window runs February 22–March 15, and the 7-day mean crosses the 61°F threshold around March 15. Cold-water starts are the cheap ones.
Closing — deadline November 21
The window opens November 11 once water leaves the algae zone; the model deadline is November 21, a week ahead of the November 29 freeze normal.
Estimated water temperature by month
This is San Marcos's typical-year water curve: the same EWMA model as the live widget, run on the 1991–2020 normals instead of this week's weather.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 51° | 52° | 58° | 65° | 72° | 80° | 83° | 85° | 83° | 75° | 65° | 56° |
Warmest water typically June–September (peaking near 86°F); heaters and covers shift any month up.
Every station tells its own story: compare this curve with San Antonio's pool season and Sherman's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Texas season index.
San Marcos pool season FAQ
When should I open my pool in San Marcos, TX?
Open by March 1 — the model places San Marcos's 61°F crossing about two weeks later, and every warm day you wait pushes the water toward the 65°F algae zone. The San Marcos opening guide has the 12-step sequence.
When should I close my pool in San Marcos?
Close by November 21: cool water keeps its winter chemistry, but freeze damage is the hard stop. The San Marcos closing guide sequences the work backward from that date.
How long is the swim season in San Marcos?
San Marcos averages 189 days a year with normal highs of 80°F or better — about 7 days earlier than the Texas median. The Texas season index ranks all 68 covered cities by the same metric.
How warm does pool water get in San Marcos?
An unheated pool near San Marcos typically peaks around 86°F in high summer and bottoms out near 50°F in winter, spending roughly 4 months at or above the 78°F comfort line most swimmers prefer. The month-by-month curve above shows the whole cycle; the methodology page explains the ±5°F error bars.
Email me when San Marcos hits the closing window
Data: NOAA 1991–2020 climate normals via San Marcos (1.1 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.