Pool season · Colorado
Denver Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
One bar, one year, one Denver pool. The season bar below draws everything the model knows — opening window, prime season, closing window — against today's date, with the working details one click away on the opening and closing pages.
Denver, CO — 104 swim days a yearEach dot on the bar is one week of Denver's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (May 4–May 25), solid teal is swim season, and hollow amber is the closing window ending October 1. The black marker is today — its position against the colors is the entire executive summary.
The Denver pool calendar
Opening — target May 11
Open by May 11 — a two-week head start on the May 25 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline October 1
The window opens September 23 once water leaves the algae zone; the model deadline is October 1, a week ahead of the October 8 freeze normal.
Estimated water temperature by month
Monthly averages of the site's water model run on Denver's own normals — the shape of a typical year, not a forecast. The widget above shows where the current year actually sits.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 32° | 32° | 38° | 46° | 53° | 64° | 73° | 74° | 69° | 57° | 45° | 35° |
The curve peaks near 75°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Colorado Springs's pool season and Fort Collins's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Colorado season index.
Denver pool season FAQ
When should I open my pool in Denver, CO?
Open by May 11 — the model places Denver's 61°F crossing about two weeks later, and every warm day you wait pushes the water toward the 65°F algae zone. The Denver opening guide has the 12-step sequence.
When should I close my pool in Denver?
Close by October 1: cool water keeps its winter chemistry, but freeze damage is the hard stop. The Denver closing guide sequences the work backward from that date.
How long is the swim season in Denver?
Denver averages 104 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 Denver?
An unheated pool near Denver typically peaks around 75°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 Denver hits the closing window
Data: NOAA 1991–2020 climate normals via Denver-stapleton (0.4 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.