I've started open water swimming, we are lucky as we have a swimming lake nearby which is controlled and there are lifeguards. ( you have to pay to swim). We also have a couple of lidos which stay open all year round. I had to do an induction course which explained the importance of acclimatisation, how to warm up safely etc. Always wear a tow float so you can be seen and never go alone. When the water has been really cold ( think ice) I always wear gloves and swimming boots so my extremities are toasty and I don't stay in too long. Some people do their swim in their wetsuit and then take a cold plunge in their swimming costume for a few seconds to get the cold sensation which is exhilarating (after you get out). These last few weeks when it has been sunny but chilly has been lovely. I think the lake temperature is now about 10 degrees. I am not going back to swimming in chlorinated, noisy, smelly indoor pools again. Its outdoors all the way.
Things you find stressful that other people don't notice.