Pool season · California
Ontario Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
Ontario'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.
The bar compresses Ontario's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the March 4–March 25 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends November 28. Wherever the today marker sits, the nearest color change is your next appointment.
The Ontario pool calendar
Opening — target March 11
Open by March 11 — a two-week head start on the March 25 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline November 28
Hold the cover until November 18, then winterize by November 28, a week ahead of the December 30 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
This is Ontario'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 56° | 56° | 59° | 62° | 66° | 70° | 77° | 80° | 80° | 74° | 66° | 58° |
Warmest water typically August–September (peaking near 80°F); heaters and covers shift any month up.
Email me when Ontario hits the closing window
Data: NOAA 1991–2020 climate normals via Ontario International Airport (1.2 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.