You can only swim in hot springs, but your bathing suit is hurt by hot spring water, so you can wear a worthless one when you go. If you feel uncomfortable, no matter how cold the water is, it won't be cold as long as it keeps moving. Don't stop. I'll feel cold if I stop. Go ashore and rest if you don't swim. The water temperature is also related to the season. I usually go swimming because of my room in winter.

The temperature will be higher. In spring and autumn, the water will feel very cold because it has just stopped warming.