Pool season · North Dakota
Bismarck Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
Bismarck'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.
Reading it takes ten seconds: 52 dots, one per week. Solid teal is Bismarck's swim season; the hollow teal run before it (May 14 to June 4) is when to open; the hollow amber run after is when to close, with September 19 as the deadline; gray is the covered season. Today's marker shows where you stand in that cycle right now.
The Bismarck pool calendar
Opening — target May 21
Open by May 21 — a two-week head start on the June 4 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline September 19
The window opens September 9 once water leaves the algae zone; the model deadline is September 19, a week ahead of the September 30 freeze normal.
Estimated water temperature by month
Monthly averages of the site's water model run on Bismarck'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 15° | 14° | 23° | 36° | 49° | 60° | 68° | 70° | 64° | 52° | 36° | 23° |
The curve peaks near 70°F — comfortable-water months here usually involve a heater or a solar cover.
Email me when Bismarck hits the closing window
Data: NOAA 1991–2020 climate normals via Bismarck 2.4 NNW (1.9 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.