Season geography
Providence sets the pace for Rhode Island: opening around Jun 4, closing around Sep 17, roughly 104 swimmable days. 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.