Honestly, it depends on where you are from and what you consider cool. While we did live in Chicago for five years we are still southerners. Folks say the pools are heated, but mostly they just warm them up slightly. They are never as warm as I would need for them to be to swim when the air temperature is cool (anything below 80 degrees, particularly with a little breeze blowing, is cool to me.) Last year we did get in the outside hot tub on Christmas Eve at WLV. My kids jumped into the pool for a few minutes but it didn't last long. No way would we ever do a water park in the late fall and winter months, you have to stand in line wet, but many folks do it. My kids would be blue! Bring the suits, but don't count on having a nice relaxing swim.