Sour Lake

Acidic hydrothermal lake along the Mud Volcano boardwalk; sulfur microbes drive the acidity.

Insider tip

Morning steam is most dramatic before crowds;

Insider tip

Keep distance from vents;

The light

Mornings can be foggy; some alpenglow on surrounding ridges when skies clear

Heads up

Acidic water can cause burns; stay on boardwalks; ground can collapse near vents; temperatures high; bear spray recommended; cell service unreliable

When to come

Best access runs June through October; mornings have softer light, but fog can obscure views, and mid-day glare plus crowds are more noticeable.

Natural Attraction

Natural AttractionOPERATIONAL★ 4.7
Thermal Feature7,000 ftMay - OctoberRestrooms availableNo permit neededGolden-hour pick

Boardwalks frame Sour Lake, a hot, acidic pool in the Mud Volcano area. The acidity comes from sulfur-oxidizing microbes, and the crust around the lake is thin and breakable. This setting sits within the Yellowstone Caldera, illustrating how hydrothermal activity and microbial life thrive in extreme chemistry.

Getting there & parking

How To Get There
Enter Yellowstone via any main gateway; drive to Mud Volcano area; park at Mud Volcano Trailhead; follow the Mud Volcano Trail boardwalk looping Sour Lake.
Distance From Entrance
Varies
Road Type
Paved roads to Mud Volcano; on-site boardwalks
Parking Availability
Mud Volcano Trailhead parking; can fill during peak season.
Peak Fill Times
Varies; peak season brings crowded lots
GPS Coordinates
44.62062, -110.436

When to go

Best Time To Visit
Best access runs June through October; mornings have softer light, but fog can obscure views, and mid-day glare plus crowds are more noticeable.
Best Visit Times
Early morning or late afternoon during summer; weekdays for lighter crowds
Sunrise Sunset Quality
Mornings can be foggy; some alpenglow on surrounding ridges when skies clear
Best Season
Summer
Busiest Season
July and August
Seasonal Access
Roads open typically late Apr/May–Oct/Nov; snow conditions determine opening
Road Opening Dates
Roads open typically late April/May through October/November
Snow Lingering
Snow may linger into May in higher elevations
Winter Access
Closed to general visitation in winter due to snow
Weather Patterns
Mornings can hold fog; heat and steam can distort air; summer thunderstorms common

What you will experience

Attraction Type
Thermal Feature
Main Features
Acidic hot pool, hydrothermal activity, fumaroles, perched water system, within Yellowstone Caldera
What Youll See
Boardwalk loops around Sour Lake; hot water; steam plumes; mineral crusts around vent rims
Unique Characteristics
Acidic lake sustained by sulfur-oxidizing microbes; perched water system within a caldera setting; part of one of the world’s largest volcanic systems
Photo Opportunities
Early morning steam with soft light; close-ups of vent rims; long shot over the boardwalk
Photography Spots
Overlooks along the boardwalk; steam plumes framed by nearby vents
Best Viewpoints
Sour Lake overlook along the Mud Volcano Trail boardwalk; keep distance from vents
Common Wildlife
Mammals like bison, elk, bears, wolves frequent Hayden Valley nearby
Best Wildlife Times
Dawn and dusk; wildlife move through open valleys near Mud Volcano
Geological Formation Type
Acidic hydrothermal lake within a hydrothermal field; perched water system; within Yellowstone Caldera
Scientific Interest
Microbial ecosystems in extreme acidity; sulfur cycle; caldera hydrothermal dynamics

Facilities, fees & access

Entry Fees
Park entrance fee applies; no separate Sour Lake fee
Permits Required
No
Restrooms Available
Yes
Restroom Type
Vault
Picnic Areas
No
Water Available
No
Cell Service
Unreliable in Mud Volcano area
Interpretive Signs
Yes
Accessibility
Boardwalks with variable gradient; consult signs for accessibility at Sour Lake section
Accessibility Level
Boardwalks accessible; gradient varies
Nearby Services
Interpretive signs; vault toilets; limited water at trailheads
Nearby Facilities
Interpretive signs; vault toilets at Mud Volcano area; no on-site drinking water
Family Friendly Notes
Boardwalks limit risk; hold hands near edges; hot water hazards

Safety

Safety Considerations
Acidic water can cause burns; stay on boardwalks; ground can collapse near vents; temperatures high; bear spray recommended; cell service unreliable

Nearby

Nearby Attractions
Mud Volcano area, adjacent geothermal zones, and the Yellowstone Caldera region.
Connecting Trails
Mud Volcano Trail loop; connections to other thermal areas along the loop
Trailheads Here
Mud Volcano Trailhead

Planning advice

Insider Tips
  • Morning steam is most dramatic before crowds;
  • Keep distance from vents;
  • Download offline maps;
  • Parking may overflow in peak season; go early or plan for overflow spots
Tips Advice
  • Stay on boardwalks; crust around Sour Lake is thin and can burn if stepped on.
  • Wear sturdy closed-toe shoes; watch for steam vents and uneven ground.
  • Cell service is unreliable; carry offline maps; Bear spray recommended in Yellowstone.

More details

Park Area
Yellowstone National Park – Mud Volcano Area
Elevation Feet
7000
Visitor Center Present
No
Guided Tours Available
No
Lake Size
Dimensions not published; Sour Lake is a small acidic pool within Yellowstone's Mud Volcano area.
Fishing Nearby
No
Swimming Allowed
No
Boating Allowed
No
Climbing Areas
No
Review Summary
Visitors rate Sour Lake highly for its intense hydrothermal exposure and clear interpretive guidance; expect crowds in peak season. The short, accessible route makes Sour Lake a practical highlight within the Mud Volcano zone, underscoring Yellowstone’s geothermal dynamism and the need for safety discipline.

Location

Sour Lake geothermal pool in Yellowstone National Park, surrounded by forested banks and steaming mineral waters.Sour Lake overlook in Yellowstone National Park, framed by evergreen forests with a broad valley, distant ridges, and a blue sky.Bison stands near the shore at Sour Lake in Yellowstone National Park, with a pine forest backdrop and bright blue sky.Sour Lake geothermal pool at Yellowstone National Park, steam rising from a blue pool surrounded by pine trees and a wooden barrier.Sour Lake overlooks a barren shore with a pine forest in the distance and dark storm clouds gathering over Yellowstone National Park.

Frequently asked questions

Do I really need to arrive before 7am to get parking?

Parking at Mud Volcano Trailhead can fill by early morning in peak season; overflow areas exist, so plan accordingly or start very early.

Is it worth the short boardwalk hike to Sour Lake?

Yes. The Mud Volcano Trail is easy and Sour Lake showcases the strongest hydrothermal-chemical interaction in the immediate area; you’ll see hot water, steam, and microbially driven acidity up close.

Can I bring my dog to the thermal area?

Dogs are not allowed on boardwalks or near thermal features; they must stay in parking areas or vehicles.

Will my 65-year-old be able to walk to Sour Lake viewpoint?

Boardwalks are generally accessible, but gradients vary; allow extra time and take breaks if needed.

Is the water actually blue, or is that just in photos?

The dominant story here is heat and acidity; the water’s appearance is not the point—focus on microbial chemistry and the steam activity.

Grand Prismatic Spring

Rainbow rim of a hot spring; colors arise from thermophiles in Yellowstone's volcanic system.

Yellowstone Lake

Caldera lake tilted by resurgent domes; hydrothermal vents dot the lakebed.

Lake Butte Overlook

Panoramic view of Yellowstone Lake from the caldera rim; distant Tetons on clear days.

Artist Point

Lower Falls overlook; canyon walls colored by hydrothermal alteration of rhyolite.

Gibbon River

84 ft Gibbon Falls; river through hydrothermal basins along Grand Loop Road.

Gibbon Falls

84-foot cascade over an ancient Yellowstone lava flow; drive-up overlook with a wheelchair-friendly path.

Sources

Editorial review: YourNPGuide Editorial Team. Information is compiled from official sources, verified traveler reviews, and editorial research; no firsthand visit is implied unless explicitly documented. Learn how YourNPGuide works.

Last updated January 2026. Report an issue.