Delaware Pool Season: Opening & Closing Dates by City

Local dates for every featured Delaware city — when the water warms up, when it cools off, and how long the season actually lasts.

City Opening window Closing window Season
Wilmington May 17 – Jun 6 Sep 10 – Sep 28 ≈ 116 days
Dover May 7 – May 28 Sep 21 – Oct 8 ≈ 135 days

Windows show the stretch when each city's daily average passes through the low-to-mid 60s°F (1991–2020 NOAA records, nearest station to each city). Click a city for its month-by-month table and full season notes.

Season geography

Across Delaware's featured cities, typical openings spread from May 18 to May 27, closings from Sep 20 to Sep 29, and the unheated season runs 116–135 days depending on where you are. Elevation, coastal water, and urban heat all pull real dates around, which is exactly why a state-level answer isn't enough.

For your exact town, the pool season lookup takes a ZIP code. Opening day itself is a chemistry job — the dosing calculator turns your first test reading of the year into exact amounts.

Delaware planning pages

When to open — Delaware When to close — Delaware All states →