I recently spent some time down in the Snowy Mountains. I was there to walk some of the tracks around Thredbo, including the walk to the summit of Mount Kosciuszko. It was a very cold week for late autumn while I was there, with temperatures ranging from -3ºC to 5ºC. There was even a snowfall up above 1900 metres, most of which was still around on my first day of walking. With temperatures like those I shied away from a swim in a very cold Thredbo River, and instead travelled to Yarrangobilly Caves where there is a thermal pool. The caves are in a karst region of the Snowy Mountains, and several are open to the public as show caves. They are within the Kosciuszko National Park. The pool was constructed to contain the waters from a hot spring emerging from the limestone. The water is 27ºC all year round. The pool is 20 metres long and deep enough to dive into (if you're that way inclined). I did several lazy lengths, feeling quite warm despite the cool mountain air.
The thermal pool
The hot spring water drains from the thermal pool and flows downhill to meet the Yarrangobilly River about twenty or more metres away. There's a small zone in the river where the waters are warmed by the hot spring water. I enjoyed sitting in this warm river pool, but then, as I swam out into the river itself, the water got colder and colder. By the time I'd crossed the swimming hole it was downright icy. This was a very quick swim indeed.
Yarrangobilly River swimming hole
I soon warmed up on the very steep half kilometre walk back up the hill to the caves themselves.
Walking back to the caves from the pool