What is the minimum water temperature for swimming workouts, like 1-2 km swims? I love swimming in lakes and rivers and am generally okay with cooler water (especially if swimming intensely), but I'm concerned about under-cooling my organs (most of all prostate and kidneys). Of course, if it feels too cold or I start freezing, I get out immediately.
It depends on your body and acclimation. I had a friend who was an excellent swimmer who died after being stranded in Lake Michigan when it was 45F. I was at a 1 and 2 mile race once where the water temperature was 68F, and it was early season so people had only acclimated with warm pool swimming. Out of 500 or so people, 3 women without wetsuits became hypothermic. They recovered with warm showers and ER visits. No men had issues and no one wearing a wetsuit had issues. I swam with no wetsuit and was fine. Men on average have more mass and about twice the muscle mass in proportion on average, and this helps them. People who are both strong and have a fat layer may also have an advantage. I have heard of people swimming distance in the San Francisco Bay daily without a wetsuit, and that is quite cold. I recommend that with boat support you start with very short swims and see how you react, and this will also allow your body to acclimate.