I just got back from the lake, where I took the temp in three different locations. I was very surprised at the results. The lowest temp I read was 72! I had one reading of 74.
The readings were made in the surface water (~6-8 inches deep), but away from the shore. One other caveat, I was using a brand new thermometer, which I purchased just this morning, as my old one was toast. I don’t know how accurate it actually was. I did speak to one of the rangers at the state park were the swim takes place, and she told me that they had measured it near the same, >70.
The weather was very hot today. I was at the lake at 10:30, and it was only 78, but I went for an hour run on the course, and it was 84 when I got back to my car. I made a couple of stops, and on the way home my car’s thermometer read 100*!!!. The predicted high for Satruday is 88, which is still 13* above normal.
By the way, they were changing the run course while I was running on it. I talked to the people doing the marking, and they said the course is exactly as the current map on the website, but the direction has been reversed. Personally, I think that’s a positive change. I prefer running the River Trail section that direction.