Sour Lake

Sour Lake is one of the intriguing hydrothermal features located in the Norris Geyser Basin region of Yellowstone National Park, a place known for having the hottest, most acidic, and most dynamic geothermal activity in the park. 

Sour Lake is a quiet yet powerful example of Yellowstone’s volatile underground world. Its surface may appear deceptively calm, but the chemistry beneath it reveals a complex and continuously evolving thermal system shaped by heat, gas, and mineral-rich water rising from deep within the Earth’s crust.

Sour Lake

Quick Reference: Sour Lake

Category	Details
Thermal Feature Type	Acidic hot spring / hydrothermal lake
Location	Norris Geyser Basin area, Yellowstone National Park
Water Temperature	Approximately 145–160°F (62–71°C), varies with underground activity
Water Characteristics	Highly acidic water with strong sulfur odor caused by hydrogen sulfide gas
Appearance	Murky, milky, and rippling surface due to gas bubbling and thermal convection
Color & Surroundings	Pale water tone with bleached mineral deposits and minimal vegetation
Activity Level	Constant gas release and roiling; does not erupt like a geyser
Notable Scientific Importance	Helps scientists monitor volcanic gas and geothermal system changes
Hazards / Safety Notes	Extremely acidic and dangerous; stay on boardwalks at all times
Typical Visit Duration	Short stop, typically 10–20 minutes
Photography Tips	Best during cool mornings for dramatic steaming effects
Accessibility	Easy walk via boardwalk; no restrooms on-site

The lake earns its name from its distinctly acidic conditions and strong sulfuric odor that drifts across the surrounding area. Visitors approaching Sour Lake will often smell the pungent scent long before reaching the water’s edge, the result of hydrogen sulfide gas rising from underground vents and reacting with surface oxygen to create sulfuric acid. This chemical process gives the water an extremely low pH, contributing to the lake’s hostile environment where very few microorganisms can survive, unlike the thermophile-rich hot springs that display bright bands of color. Instead, Sour Lake typically appears murky or milky in tone, its surface rippling gently with convection currents and gas bursts that stir sediment from the vent below.

Sour Lake’s acidic water has shaped the landscape around it dramatically over time. The mineral-rich runoff dissolves surrounding rock and sinter, etching out irregular formations and leaving behind bleached, barren ground where vegetation struggles to grow. Small fumaroles release steam at the edges of the lake, indicating the presence of a powerful underground heat source that remains hidden despite the lack of explosive activity. This subtle but continuous activity provides scientists with valuable data about the thermal plumbing system beneath Norris, one of the most scientifically monitored areas in Yellowstone.

The area surrounding Sour Lake feels remote and otherworldly despite being close to major visitor pathways. Visitors standing safely on the designated boardwalks can observe the lake’s textured shoreline and swirling surface, experiencing firsthand the uneasy balance between beauty and hazard that defines Yellowstone’s thermal landscapes. Because the water is acidic enough to dissolve organic tissues, it is essential that visitors never leave the boardwalks or attempt to touch the water.