Picchio is an organization located within Hoshino Resorts in Karuizawa city, Nagano prefecture. It is, among other activities, offering different tours focused on nature and wildlife throughout the whole year. During summertime only, it is possible to join a two hours long tour to play in the Yu river, a river that crosses Hoshino Resorts. Get your shorts and your waterproof shoes (as well as some towels and spare clothes) ready!
In Japanese, Yu river is written 湯川. The first character is the one for "hot water" and 川 is the character for "river". It is located right next to Hoshino Resorts' hot springs and when you look at it from a bridge, you can see steam floating above the waters. Which is why at first glance, anyone would logically think that the waters of the Yu river are nice and warm. Well, too bad.
Nagano prefecture is a mountainous region. Even during summer, the weather doesn't get as hot as it can in some parts of Japan. Because of that, the temperature of the waters is 10°C on average. It may get up to 15°C, but only during very hot periods. Since August is generally hotter than July, I would maybe recommend to take part in the tour then.
I'm not going to lie; the first minutes are painful. The water is extremely cold and even if the guides keep repeating that you will soon be used to it, the only thing you want to do is leave and rush to the hot springs. After a while though, you will eventually feel better and you will start to think that it's not a big deal if your trousers gets a little wet after all. Simply enjoy yourself, but try not to fall in the water!
Before the tour ends, it's time for a break somewhere the waters are calm to look for insects and fish that live there. The easiest one to find is the Japanese fluvial sculpin, a fish that lives in cold water. It hides between rocks, so open your eyes wide and try to catch one!
If you have made it through the 300-meter walk in the Yu river, congratulations: you now deserve your bath at the hot springs!