Is low 70s considered reasonable swimming weather? Don't know about Florida, but in NJ 70s to me is a bit too cold to be swimming.
I'm a born, raised in the south, pure bred Southerner who loathes cold weather. This grandma doesn't do cold. My husband and I took our then 3 y/o GS to WDW last Feb 4th-11th. I'm not sure what the temperature was, but it was warm enough we southerners wore shorts and swam every day. If it'd been cold, there is no way I'd have gotten anywhere near that pool.
I told this story here on the DIS when I got back when someone asked about funny kids, but it fits here too: The night before we were due to fly back to Texas, my D-I-L called to tell me that it was cold here and to be sure and put the jeans my grandson wore down to Florida back on him and to please buy him a warm hoodie for the plane. Taking her advice I put long pants on me and him both, and made sure he had a cute WDW hoodie to put on just before we landed at DFW. My stubborn husband wore his shorts all day and then wore them home. When my son and D-I-L picked us up in Dallas that night at baggage claim, my grandson was happily chattering to them about how much fun he'd had and how he wanted to go back and not really paying attention to anything going on around him. Just as we got to the doors that lead outside to the parking garage, they opened, and a blast of cold air hit him. His chattering came to a sudden screeching halt, his eyes got huge, he opened his mouth to a perfect O, shuddered, and without saying a word, turned and literally ran back inside and toward the moving doors where you come out from the gates to baggage claim. He was running full speed and wouldn't stop, so we had to literally chase him down.
When we caught him and asked what the heck he was doing, he very loudly yelled, "I'm getting back on that plane. I wanna go back to Disney World where it's warm and I can go swimming every day!". All the other travelers still in there heard him and died laughing at him. I reminded him we'd just been and he hadn't seen his parents for a week, and didn't he want to spend some time with them. He glanced at his parents, then without hesitation, he said, "I saw them, now I wanna go back to Disney World. It's too cold here! Take me back to Mickey Mouse now!".