YELLOWSTONE – The Boiling River, a hot spring that joins the Gardner River in Yellowstone’s Mammoth area, is gradually getting hotter. The spot is a popular swimming area in the late summer through winter.

Park spokeswoman Amy Bartlett told KSL News that the temperature of the thermally heated water has been increasing slightly since August of last year. That month, the temperature was approximately 134 degrees Fahrenheit. The last in February 2015, the temperature has ranged from about 136.5 to 139.5 degrees.

Too Hot to Swim?

Water that is 120 degrees Fahrenheit  is considered to be scalding so the Boiling River is too hot to swim in this year. However, where the Boiling River meets the Gardner River, cool water may dilute the hot spring water enough to be safe.

Longtime locals swimming at Boiling River on Feb. 22 told Livingston EnterpriseManaging Editor Justin Post the water seemed hotter than they’ve ever remembered it. A small cascade of hot water which in the past has been pleasant to sit under was unapproachably hot one recent Sunday, Post said.

And a loose rock berm, built up informally by swimmers over the years, used to be at the edge of a cold water “no man’s land” in the winter. On Sunday, swimmers were sitting on those rocks and even on the other side of them, Post said.

Park geologists aren’t sure why the temperature is escalating. It could be that cold water flowing into the Boiling River through underground sinkholes is being blocked or diverted somehow.

Another explanation for the perceived increase in temperature could be that the Gardner River itself is at lower seasonal flow rates, which means less cold water to dilute the hot.

See more information, map, and a video about the Boiling River Swimming Area