Pool season · California
Castro Valley Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
Castro Valley'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.
Each dot on the bar is one week of Castro Valley's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (April 28–May 19), solid teal is swim season, and hollow amber is the closing window ending November 7. The black marker is today — its position against the colors is the entire executive summary.
The Castro Valley pool calendar
Opening — target May 5
Target May 5; the practical window runs April 28–May 19, and the 7-day mean crosses the 61°F threshold around May 19. Cold-water starts are the cheap ones.
Closing — deadline November 7
Hold the cover until October 28, then winterize by November 7, a week ahead of the December 25 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
Monthly averages of the site's water model run on Castro Valley'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 51° | 52° | 55° | 57° | 60° | 63° | 66° | 67° | 68° | 66° | 60° | 53° |
The curve peaks near 68°F — comfortable-water months here usually involve a heater or a solar cover.
Email me when Castro Valley hits the closing window
Data: NOAA 1991–2020 climate normals via Hayward Air Terminal (4.7 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.