Boiling River

The Boiling River Trail is a one-mile trail located near the "45th Parallel," about halfway between the northeast entrance in Gardiner and Mammoth Hot Springs. When the water levels are low enough for swimming to be permitted, you can enjoy the river water warmed by geothermal activity deep underground. - See more at: http://www.ypf.org/site/News2?page=NewsArticle&id=5107#sthash.dgFYNPPm.dpuf