Pool season · State index
Colorado Pool Season Calendar
Last updated: July 15, 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.
| 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.