Two tourists have been filmed waking across the protected thermal area surrounding the largest hot spring in the US, prompting widespread criticism after footage of the act spread online.

The pair were seen leaving the designated boardwalk and crossing the colourful bacterial mats that surround the Grand Prismatic Spring in Wyoming’s Yellowstone National Park, despite the area being off-limits.

Montana woman, Tanya Saueressig, was standing on the boardwalk at the time enjoying the natural scenery before she spotted the “oblivious” tourists.

“It was a really nice crowd,” she told Cowboy State Daily.

“People on the boardwalk were being lovely, giving each other space, and being quiet. It was a really nice experience.”

Ms Saueressig said she was mortified to see two people waking close to the hot spring’s scalding-hot water.

“I stopped in my tracks and was like, ‘Is that people? That can’t be people. Nobody’s that dumb,’” she added.

“You could tell they were just strolling along, taking their selfies, without a care in the world.”

Park rules require visitors to stay on marked boardwalks and trails at all times as water beneath the thin surface crust can reach near-boiling temperatures, making the geothermal areas extremely dangerous if the ground gives way.

But it wasn’t just the tourists’ safety Mr Saueressig was worried about, the landmark’s vivid orange, yellow and green hues are created by heat-loving micro-organisms that live on the bacterial mats, which can be permanently damaged by a single footprint.

“They were totally oblivious to what was right under their feet. You’re causing so much damage with every step you take, and you don’t care,” she said.

“I started getting scared because I thought they were going to fall in and get really, really hurt.

“I worried people at the overlook were going to watch someone die that day. They were out there where nobody could help them.”

The latest incident has reignited frustrations over visitors repeatedly ignoring park regulations.

In July 2025, a man wear thongs was seen trampling over the bacteria mats to collect his hat which had blown off his head.

Last year a bison boiled to death after stumbling into the Grand Prismatic Spring’s scalding water.

Walking on the mats is consider “thermal trespassing” and people found breaching the rule can be issued with a fine, park ban or even jail time.