Ninemeyer Hot Springs

Boise County, Idaho · Near Idaho City
43.7550°N, 115.5710°W · 3,760 ft
169°F 35°F air · Good soaking weather 3,760 ft Open Short Walk US Forest Service Camping nearby (0.1 mi)
Very Hot Source, Use Extreme Caution

At 169°F, the source water at Ninemeyer Hot Springs is hot enough to cause burns. Some hot springs this hot have cooler side pools or downstream areas suitable for soaking. Always test the water temperature before entering.

Aerial view of the ground around Ninemeyer Hot Springs LiDAR bare-earth view of the same ground around Ninemeyer Hot Springs
Aerial LiDAR bare earth

Drag the handle to compare the two views. The orange dot marks the spring, in a frame about three quarters of a mile wide.

Ninemeyer Hot Springs is scalding. The source temperature is far above anything a person can enter, hot enough to cause serious burns on contact. It sits in the Boise National Forest, in Boise County, a short walk off Middle Fork Road and about fourteen miles from Idaho City, with Ninemeyer Campground a stone's throw away. Access is open. The water sampled in 1982 was strongly alkaline.

Location

Forest land a little under four thousand feet up. A wet climate for Idaho, and a normal winter brings ten feet of snow, so expect deep snow across the cold months. From Middle Fork Road the walk is short. The campground is nearer still. Forest Service land throughout, and nothing in the record about the ground itself.

The season flag points to midwinter, though at this temperature the season matters less than the water itself. Do not get in at the source. Look for a place where it has mixed with cold water and test it with a hand before anything else. Camp at Ninemeyer Campground, right there. There is no fee entry.

Terrain

Aircraft with laser scanners measured this ground to within inches. The scan strips out trees and buildings, leaving the bare shape of the land around Ninemeyer Hot Springs.

Setting
Hillside
The spring sits on a steep slope that climbs to the south.
Highest ground nearby
648 ft above the spring
Within a quarter mile, to the south
Cross-section through the spring

A slice through the ground from northwest to southeast, about 0.6 miles end to end.

Elevation data: USGS 3D Elevation Program. Aerial imagery: USGS The National Map. Public domain.

Heat Below
139 milliwatts per square meter of heat flow

That's about twice the US average of 65. It's higher than at 88% of the springs on this site.

Heat flow measures the warmth working its way up through the ground from deep inside the earth. Where it runs high, rain and snowmelt that seep down through cracks in the rock come back up hot.

Heat flow estimate: Stanford Thermal Earth Model (Aljubran & Horne, 2024), CC BY 4.0.

Monthly Climate
29°
Jan
31°
Feb
38°
Mar
43°
Apr
53°
May
64°
Jun
75°
Jul
74°
Aug
63°
Sep
49°
Oct
36°
Nov
27°
Dec
Annual Precip: 30.1 in Annual Snow: 122.0 in
Best Time to Visit
December Air 27°F · Water 169°F · +142° contrast
January Air 29°F · Water 169°F · +140° contrast
February Air 31°F · Water 169°F · +138° contrast
December offers 48°F more contrast than July
Current Conditions
35°F
S 0.0 mph 93% Good soaking weather
Tuesday 76° Low 41° Sunny
Spring is +93° warmer
Wednesday 82° Low 48° Sunny
Spring is +87° warmer
Thursday 74° Low 52° Showers And Thunderstorms Likely 73% precip
Spring is +95° warmer
Friday 74° Low 48° Mostly Sunny then Slight Chance Rain Showers 20% precip
Spring is +95° warmer
Saturday 77° Low 47° Sunny 5% precip
Spring is +92° warmer
Water Chemistry Sampled 1982-08-19

The water at Ninemeyer Hot Springs is alkaline (pH 9.6) with 245 mg/L total dissolved solids.

pH 9.6 Alkaline
pH influences mineral absorption through skin
Higher mineral concentration for therapeutic soaking
Calcium 2 mg/L
May support bone density and joint health
Magnesium 0 mg/L
Known for muscle relaxation and stress relief
Sodium 64 mg/L
Supports circulation and skin hydration
Sulfate 28 mg/L
Traditionally used for skin conditions and inflammation
Chloride 2 mg/L
Natural antiseptic with skin health benefits
Nearby Camping
Nearby Camping
Ninemeyer Campground 0.1 mi away

Overview:Due to a wildfire, there are no amenities at the campground.  Currently there are no developed campfire rings therefore when Stage 1 fire restrictions area in effect, no fires are permitted.A stay at Ninemeyer Campground enables guests to enjoy all the beauty and recreation offered along the (Middle Fork Boise River Road) Forest Service (FS) Road 268. Weather is usually good from mid-May through late September and is easily accessible by car in good weather, although the road is some...

Reserve on Recreation.gov →
Temperature
169°F
Warm Hot Boiling
Water Temp 169°F (76°C)
Avg Air Temp 49°F
Above Ambient +121°F
Great soaking conditions September
Access
Open
Road Access Short Walk
Nearest Road Middle Fork Road
Distance to Road 440 ft
Land
Ownership Federal
Agency US Forest Service
Designation National Forest
Unit Boise National Forest
Manager US Forest Service
Protection 3 - Protected, subject to extractive use
Frequently Asked Questions
What is the water temperature at Ninemeyer Hot Springs?
Ninemeyer Hot Springs has a water temperature of 169°F (76°C). This is considered a hot spring, well above body temperature.
Where is Ninemeyer Hot Springs located?
Ninemeyer Hot Springs is located in Boise County, Idaho at 3,760 feet elevation, near Idaho City. Coordinates: 43.7550°N, 115.5710°W.
How do I get to Ninemeyer Hot Springs?
Ninemeyer Hot Springs has Short Walk road access, with the nearest road being Middle Fork Road (440 ft from the road).
Is Ninemeyer Hot Springs free to visit?
Ninemeyer Hot Springs has Open access. It is managed by US Forest Service.
Can I camp near Ninemeyer Hot Springs?
Yes, Ninemeyer Campground is located nearby (0.1 miles away).
What minerals are in the water at Ninemeyer Hot Springs?
Water chemistry analysis shows the presence of pH, Total Dissolved Solids, Calcium, Magnesium, Sodium, Sulfate, Chloride. The pH is 9.6 (alkaline). Total dissolved solids measure 245 mg/L.
Is it safe to soak at Ninemeyer Hot Springs?
No, not at the source. The water at Ninemeyer Hot Springs reaches 169°F, which can cause severe burns within seconds. Look for cooled side pools or downstream stretches, and test with a hand before anything else.