Updated July 2026
South Fork Plunge
Do not enter this water
At 129°F this water is at or above the temperature that causes serious burns within seconds. Springs in this range are frequently vents, geysers, or boiling pools and are for viewing only.
What this number is, and is not
129°F is the maximum surface temperature measured at the vent during the USGS/NOAA thermal springs survey (1965–1980). It is not a current reading, and the temperature of any pool downstream of a vent is almost always lower.
This page also records nothing about access. Land ownership, legal entry, trail conditions, and whether a usable pool exists are all outside this dataset. Confirm with the managing agency before setting out.
Graded lakes within 25 miles
- CCascade R Lake · Valley County · 19 mi
- BCascade Reservoir A Sugar Loaf Island · Valley County · 19.2 mi
- BCascade R W of Sugarloaf Island Lake · Valley County · 19.5 mi
- BCascade Reservoir · Valley County · 19.6 mi
Nearby hot springs
- ScaldingMollys Hot Spring0.7 mi · 138°F
- ScaldingTrail Creek Hot Spring2.6 mi · 122°F
- ScaldingVulcan Hot Springs4.4 mi · 190°F
- CoolDollar Creek Warm Spring5.9 mi · 68°F
- ScaldingGold Fork Hot Spring12.5 mi · 127°F
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Frequently Asked Questions
South Fork Plunge was recorded at 129°F (54°C), which classifies as Scalding (above 113°F (45°C)). Dangerously hot: at or above 113°F, water can cause serious burns within seconds. Many springs this hot are vents, geysers, or boiling pools meant for viewing only — do not enter. That figure is the maximum surface temperature measured at the vent during the USGS/NOAA survey between 1965–1980 — not a current reading, and not the temperature of any pool downstream of the vent.
We can't tell you that, and at 129°F the question is largely settled by the temperature itself: this is above the 104°F ceiling health agencies recommend for hot water. At this temperature water can cause serious burns within seconds, and springs this hot are frequently vents or boiling pools meant for viewing only. Separately, this inventory records no information about land ownership, legal access, or whether a usable pool exists.
South Fork Plunge is in Idaho at approximately 44.6320, -115.6970. The nearest graded lake is Cascade R Lake, about 19 miles away. Coordinates come from the USGS/NOAA inventory and locate the vent, not a trailhead or parking area.
Source: USGS/NOAA Thermal Springs List for the United States, via PANGAEA (CC-BY-4.0). Compilation: USGS Waring 1965 / Muffler 1979 + NOAA NGDC KGRD-12 (1980).
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