Pool season · State index
Colorado Pool Season 2026: Opening & Closing Dates by City
Last updated: July 25, 2026 · 19 cities covered
Both halves of the pool year for all 19 covered Colorado cities. The median calendar runs May 13 to October 1. Every row links to a one-page season overview with the live water-temperature model; the opening and closing hubs carry the full checklists.
Colorado: a short-season pool state| City | Open by | Close by | 80°F+ days |
|---|---|---|---|
| Arvada | May 14 | Sep 28 | 99 |
| Aurora | May 15 | Oct 1 | 105 |
| Boulder | May 14 | Sep 28 | 98 |
| Broomfield | May 9 | Oct 4 | 109 |
| Castle Rock | May 19 | Sep 25 | 85 |
| Centennial | May 16 | Sep 30 | 89 |
| Colorado Springs | May 13 | Oct 1 | 90 |
| Denver | May 11 | Oct 1 | 104 |
| Fort Collins | May 12 | Sep 30 | 92 |
| Grand Junction | Apr 26 | Oct 12 | 120 |
| Greeley | May 6 | Oct 1 | 115 |
| Highlands Ranch | May 16 | Sep 30 | 89 |
| Lafayette | May 9 | Oct 4 | 109 |
| Lakewood | May 16 | Sep 29 | 82 |
| Longmont | May 13 | Sep 28 | 105 |
| Loveland | May 17 | Sep 24 | 98 |
| Pueblo | May 2 | Oct 2 | 125 |
| Thornton | May 9 | Oct 4 | 109 |
| Westminster | May 9 | Oct 4 | 109 |
What the columns mean
"Open by" is the recommended spring date — two weeks before the city's 7-day mean temperature crosses 61°F, the model's proxy for water approaching the 65°F algae-growth zone. "Close by" is the fall deadline — ten days after the water leaves that zone, capped a week ahead of the local 50% first-freeze date. "80°F+ days" counts days whose normal high reaches 80°F: the length of the true warm-swim season, and the fairest single number for comparing Colorado cities against each other.
Every figure comes from each city's own NOAA 1991–2020 normals station (named in its guide's footer), so neighboring cities can legitimately differ by a few days. The season overview linked from each row adds the live water-temperature model and the full-year season bar; the state hubs above carry the step-by-step checklists.
Swim-season length across Colorado
The fairest way to compare Colorado cities is the number of days with 80°F+ normal highs — the practical warm-swim season. Every bar links to that city's one-page season overview with the live water model.
Colorado pool climate at a glance
High-altitude sunshine is intense but nights stay cool, so mountain and Front Range pools run short seasons bracketed by late-spring and early-fall snow chances. In model terms that makes Colorado a short-season state. The spread shows up clearly on the local pages: compare Pueblo's pool season with Denver's and the difference is measured in weeks, not days. Neighbors in the index run on their own normals too — see California and Connecticut for the adjacent calendars.
Colorado pool season FAQ
When do pools open in Colorado?
Model openings in Colorado run from April 26 in Grand Junction to May 19 in Castle Rock, with the statewide median on May 13. Each date is two weeks before that city's 7-day mean temperature crosses 61°F — early enough to start up in algae-cold water.
When should you close a pool in Colorado?
The median Colorado closing deadline is October 1, and every city's own deadline is capped a week ahead of its NOAA 50% first-freeze date. Closing late and cold beats closing early and warm — cool water holds its winter chemistry far better.
Which Colorado city has the longest swim season?
Pueblo leads with 125 days of 80°F+ highs per year, while Lakewood brings up the rear at 82 days. The chart above ranks every covered city by the same metric.