Hot Springs in the United States

This is a classification of a measured temperature, not a soak recommendation and not a safety clearance. The "Ideal" band stops at 104°F (40°C) because that is the ceiling health agencies including the CDC and CPSC recommend for hot water. Anything above it is labelled Hot or Scalding and treated as a hazard: at 113°F and up, water can cause serious burns in seconds, and many springs that hot are vents, geysers, or boiling pools meant for viewing only.

They are not current. The source is the USGS/NOAA Thermal Springs List for the United States, compiled between 1965 and 1980 (USGS Waring 1965, Muffler 1979, NOAA NGDC KGRD-12). Each figure is the maximum recorded temperature at the vent at the time of survey. Springs change, and the temperature of a pool downstream of a vent is almost always lower than the vent itself. Treat these as a historical reference inventory, never as today's reading.

Because they have no recorded temperature. Roughly 181 springs in the inventory are named and located but were never measured. They appear in the state lists for completeness but get no detail page and no tier — we do not estimate a temperature or default an unmeasured spring to a passing classification.

This inventory says nothing about access, ownership, or legality. Many listed springs sit on private land, inside protected thermal features where entry is prohibited, or in terrain with no trail. Always confirm land status and any local restrictions with the managing agency before setting out.

Because they are part of the same trip. LakeQuality grades lake water quality across the US and tracks water temperature, and a large share of these springs sit within 25 miles of a graded lake — so the spring pages and the lake pages link to each other instead of living on separate sites.