According to Official Guinness Records,
The deepest geothermal hot spring measured by a plumb line is 305.41 m (1,002 ft), and is located at The Springs Resort and Spa (USA) in Pagosa Springs, Colorado, USA. The spring was measured on 20 August 2011.
The spring was measured by a hydrologist from Basin Engineering in Durango, Colorado. The actual depth of the spring is unknown, as the plumb line measured a maximum depth of 1,002 ft, and it ran out before hitting the bottom of the spring.
For a complete list of 2011 records, please visit 2011 Guinness Records in United States.