Pool season · State index
New Hampshire Pool Season 2026: Opening & Closing Dates by City
Last updated: July 25, 2026 · 4 cities covered
Both halves of the pool year for all 4 covered New Hampshire cities. The median calendar runs May 20 to September 28. Every row links to a one-page season overview with the live water-temperature model; the opening and closing hubs carry the full checklists.
New Hampshire: a short-season pool state| City | Open by | Close by | 80°F+ days |
|---|---|---|---|
| Dover | May 22 | Sep 25 | 41 |
| Manchester | May 18 | Sep 29 | 48 |
| Nashua | May 13 | Oct 1 | 76 |
| Portsmouth | May 22 | Sep 27 | 39 |
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 New Hampshire 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 New Hampshire
The fairest way to compare New Hampshire 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.
New Hampshire pool climate at a glance
Northern New England cold keeps the season short and sweet: pools open around mid-June and close by early September, with the White Mountains cooler still. In model terms that makes New Hampshire a short-season state. The spread shows up clearly on the local pages: compare Nashua's pool season with Dover's and the difference is measured in weeks, not days. Neighbors in the index run on their own normals too — see Nevada and New Jersey for the adjacent calendars.
New Hampshire pool season FAQ
When do pools open in New Hampshire?
Model openings in New Hampshire run from May 13 in Nashua to May 22 in Portsmouth, with the statewide median on May 22. 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 New Hampshire?
The median New Hampshire closing deadline is September 29, 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 New Hampshire city has the longest swim season?
Nashua leads with 76 days of 80°F+ highs per year, while Portsmouth brings up the rear at 39 days. The chart above ranks every covered city by the same metric.