Pool season · State index
North Dakota Pool Season 2026: Opening & Closing Dates by City
Last updated: July 25, 2026 · 2 cities covered
Both halves of the pool year for all 2 covered North Dakota cities. The median calendar runs May 17 to September 20. Every row links to a one-page season overview with the live water-temperature model; the opening and closing hubs carry the full checklists.
North Dakota: a short-season pool state| City | Open by | Close by | 80°F+ days |
|---|---|---|---|
| Bismarck | May 21 | Sep 19 | 45 |
| Fargo | May 13 | Sep 21 | 48 |
What the columns mean
"Open by" is the recommended spring date — two weeks before the city's 7-day mean temperature crosses 61°F, the model's proxy for water approaching the 65°F algae-growth zone. "Close by" is the fall deadline — ten days after the water leaves that zone, capped a week ahead of the local 50% first-freeze date. "80°F+ days" counts days whose normal high reaches 80°F: the length of the true warm-swim season, and the fairest single number for comparing North Dakota cities against each other.
Every figure comes from each city's own NOAA 1991–2020 normals station (named in its guide's footer), so neighboring cities can legitimately differ by a few days. The season overview linked from each row adds the live water-temperature model and the full-year season bar; the state hubs above carry the step-by-step checklists.
Swim-season length across North Dakota
The fairest way to compare North Dakota cities is the number of days with 80°F+ normal highs — the practical warm-swim season. Every bar links to that city's one-page season overview with the live water model.
North Dakota pool climate at a glance
Among the harshest pool climates in the nation: brutally cold winters and short, breezy summers keep outdoor swimming to roughly June through August at best. In model terms that makes North Dakota a short-season state. The spread shows up clearly on the local pages: compare Fargo's pool season with Bismarck's and the difference is measured in weeks, not days. Neighbors in the index run on their own normals too — see North Carolina and Ohio for the adjacent calendars.
North Dakota pool season FAQ
When do pools open in North Dakota?
Model openings in North Dakota run from May 13 in Fargo to May 21 in Bismarck, with the statewide median on May 21. Each date is two weeks before that city's 7-day mean temperature crosses 61°F — early enough to start up in algae-cold water.
When should you close a pool in North Dakota?
The median North Dakota closing deadline is September 21, and every city's own deadline is capped a week ahead of its NOAA 50% first-freeze date. Closing late and cold beats closing early and warm — cool water holds its winter chemistry far better.
Which North Dakota city has the longest swim season?
Fargo leads with 48 days of 80°F+ highs per year, while Bismarck brings up the rear at 45 days. The chart above ranks every covered city by the same metric.