Frying Pan Lake (renamed Waimangu Cauldron in 1963[1] though not widely used) is the world's largest hot spring. It is located in the Echo Crater of the Waimangu Volcanic Rift Valley, New Zealand and its acidic water maintains a temperature of about 50–60 °C (122–140 °F).

The Lake covers 38,000 square meters in part of the volcanic crater and the shallow lake is only 18 feet deep, but at vents, it can go down to 60 feet. 

Echo Crater was formed as part of the 1886 Mount Tarawera eruption, which opened several craters along a 17-kilometre (11 mi) rift stretching southwest from Mount Tarawera to the nearby Southern Crater. After this event, the crater's floor partly filled with rainwater and heated groundwater, but it was not until after a large eruption in Echo Crater on 1 April 1917 that the resulting larger crater filled up from hot springs to reach its current size by mid 1918.

According to en.wikipedia