Same here- I grew up in Minnesota. We would watch the thermometer on the porch, as soon as it hit 80 degrees (usually mid-June back in the 1970's), we went to the lake, which had to be all of 50 degrees that early. I remember it being soooo cold, we would jump in and swim out a floating platform as fast as we could, then soak up that "super hot" (ha!) sunshine till we quit shivering, then jump in and swim for the shore. Warm up on the shore, then repeat until we were icy little prunes.
Now I am such a wimp. We got our pool in mid-August, and swam to mid-Oct. I was very sick this fall, and it was windy a lot, so I only swam when it the water was about 80 plus. I am going to try to get a little tougher this year and start getting in when it is in the mid-upper 70's. We are working on installing our solar heater, so not sure exactly when that will happen. If I have to, I can wear my snorkeling skins and be comfortable. It was 82 degrees here yesterday, but the water is 60 degrees-too cold for me.
Spring is a tough time of the year in Texas. It can be 90+ degrees outside, and swimming sounds so good, but the water is still pretty cold. I guess I can just dunk myself in to get cooled off then go back to whatever I am doing- get hot and sweaty again, and repeat. I hope the solar can bring the temp up enough to make it swimmable when we get these spring hot sunny spells. The sun is certainly hot enough on those kinds of days.