Welcome jules!
We swim in our pond all summer. I had the water tested when we first moved here 3 years ago because I was worried about the proximity to our septic bed and stuff like that. They tested for bacteria levels and e coli just as if it was a public beach. The lab guy told me "ya can drink this stuff. It is cleaner than some folks well water"!
The water temperature fluctuates on the surface between about 68 to 78 degrees all summer and is very clear. I love it! Anything over about 73 and I can stay in there snorkelling for hours!
It is nice to dive deeper and feel the cooler bottom waters as well.

I too would be more concerned about swimming in public pools and hot tubs. That is like swimming in someone else's bathwater! Bring on the fish and frog pee!