Pool season · Illinois
Round Lake Beach Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
Round Lake Beach'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 Round Lake Beach'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 2. The black marker is today — its position against the colors is the entire executive summary.
The Round Lake Beach pool calendar
Opening — target May 11
Target May 11; the practical window runs May 4–May 25, and the 7-day mean crosses the 61°F threshold around May 25. Cold-water starts are the cheap ones.
Closing — deadline October 2
The window opens September 22 once water leaves the algae zone; the model deadline is October 2, a week ahead of the October 23 freeze normal.
Estimated water temperature by month
This is Round Lake Beach'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 24° | 23° | 31° | 42° | 53° | 64° | 72° | 72° | 68° | 58° | 45° | 33° |
The curve peaks near 73°F — comfortable-water months here usually involve a heater or a solar cover.
Email me when Round Lake Beach hits the closing window
Data: NOAA 1991–2020 climate normals via Lake Villa 2ne (3.7 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.