Pool season · Idaho
Boise Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
This is the one-page view of Boise's pool year: both model windows, the estimated water-temperature curve, and today's live position on the season bar. The detailed checklists live on the opening and closing guides; this page is the calendar you check between them.
Boise, ID — 96 swim days a yearThe bar compresses Boise's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the April 29–May 20 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends October 9. Wherever the today marker sits, the nearest color change is your next appointment.
The Boise pool calendar
Opening — target May 6
Target May 6; the practical window runs April 29–May 20, and the 7-day mean crosses the 61°F threshold around May 20. Cold-water starts are the cheap ones.
Closing — deadline October 9
The window opens September 29 once water leaves the algae zone; the model deadline is October 9, a week ahead of the October 21 freeze normal.
Estimated water temperature by month
This is Boise'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° | 34° | 42° | 48° | 56° | 64° | 73° | 78° | 71° | 60° | 46° | 35° |
Warmest water typically August–August (peaking near 79°F); heaters and covers shift any month up.
Every station tells its own story: compare this curve with Nampa's pool season and Coeur d'Alene's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Idaho season index.
Boise pool season FAQ
When should I open my pool in Boise, ID?
Target May 6. That date backs off two weeks from the day Boise's 7-day mean temperature reaches 61°F, so you start up in cold, algae-resistant water. Work the full checklist in the Boise opening guide.
When should I close my pool in Boise?
The closing deadline is October 9 — late enough that the water has cooled out of the algae zone, early enough to beat Boise's first-freeze normal by about a week. See the Boise closing guide for the winterizing steps.
How long is the swim season in Boise?
Boise averages 96 days a year with normal highs of 80°F or better — right on the statewide median. The Idaho season index ranks all 5 covered cities by the same metric.
How warm does pool water get in Boise?
An unheated pool near Boise typically peaks around 79°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 Boise hits the closing window
Data: NOAA 1991–2020 climate normals via Boise Air Terminal (2.4 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.