Pool season · Colorado
Fort Collins Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
Fort Collins'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.
Fort Collins, CO — 92 swim days a yearReading it takes ten seconds: 52 dots, one per week. Solid teal is Fort Collins's swim season; the hollow teal run before it (May 5 to May 26) is when to open; the hollow amber run after is when to close, with September 30 as the deadline; gray is the covered season. Today's marker shows where you stand in that cycle right now.
The Fort Collins pool calendar
Opening — target May 12
Target May 12; the practical window runs May 5–May 26, and the 7-day mean crosses the 61°F threshold around May 26. Cold-water starts are the cheap ones.
Closing — deadline September 30
Hold the cover until September 20, then winterize by September 30, a week ahead of the October 7 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
This is Fort Collins'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 31° | 32° | 38° | 46° | 53° | 63° | 71° | 73° | 67° | 56° | 44° | 34° |
The curve peaks near 73°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Denver's pool season and Grand Junction's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Colorado season index.
Fort Collins pool season FAQ
When should I open my pool in Fort Collins, CO?
Target May 12. That date backs off two weeks from the day Fort Collins's 7-day mean temperature reaches 61°F, so you start up in cold, algae-resistant water. Work the full checklist in the Fort Collins opening guide.
When should I close my pool in Fort Collins?
The closing deadline is September 30 — late enough that the water has cooled out of the algae zone, early enough to beat Fort Collins's first-freeze normal by about a week. See the Fort Collins closing guide for the winterizing steps.
How long is the swim season in Fort Collins?
Fort Collins averages 92 days a year with normal highs of 80°F or better — right on the statewide median. The Colorado season index ranks all 19 covered cities by the same metric.
How warm does pool water get in Fort Collins?
An unheated pool near Fort Collins typically peaks around 73°F in high summer and bottoms out near 31°F in winter, never quite reaching the 78°F comfort line without a heater or solar cover. The month-by-month curve above shows the whole cycle; the methodology page explains the ±5°F error bars.
Email me when Fort Collins hits the closing window
Data: NOAA 1991–2020 climate normals via Ft Collins (2.2 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.