It's the most dangerous swim Lewis Pugh had ever attempted, but not his first.

The former lawyer turned endurance swimmer finished a swim in the Antarctic waters off the coast of King Edward Cover near Grytviken, South Georgia, on Tuesday. Beginning at approximately 2 p.m. EST, Pugh swam in nothing but a Speedo through the icy waters. It took him 19 minutes to swim one kilometer, through waters that averaged roughly two degrees Celsius.

Had the water not been salty, it would have already been frozen. And Pugh, 48, risked dangerous hypothermia during his endeavor. Without training, it's possible to sustain serious injury or worse by swimming through these waters.

Pugh's team of supporters live tweeted his swim. After the halfway mark, Pugh passed two elephant seals, a species that can weigh over 8,000 pounds. Passing this potential danger unscathed, Pugh's speed began to drop as he went. In water that cold, his body temperature falls rapidly.

Just 200 metres to go! This is when Lewis needs to keep up the pace – his core body temperature will be dropping rapidly. #Antarctica2020 pic.twitter.com/ZBKAYToGvz — Lewis Pugh (@LewisPugh) November 7, 2017

"I hate swimming in ice cold water," Pugh said in a phone interview following his swim. People tend to assume he attempts such feats because he's especially adept or accustomed to cold water, he said. "I swim in the water to carry a message."

This dramatic feat of endurance isn't just a test of Pugh's physical strength. As a United Nations Patron of the Oceans, Pugh devotes his life to calling attention to issues facing the world's oceans.

His swim comes as the U.K. government plans to review protections for the 193,000 square miles of water the South Sandwich Islands. Currently, the region is a sustainable use marine protected area, which allows some fishing. But beginning later this month, the government will consider fully protecting the region by outlawing all fishing.

According to Simon Reddy, director of the Pew Bertarelli Ocean Legacy Project in the UK, one of the groups advocating for the region's full protection, the review is a chance to "future-proof" the remote waters from more possible exploitation later. At the moment, only small-scale tooth fishing is conducted in the region. Due to its relatively remote location and inhospitable shores, the region has largely been spared from large fishing operations.

"This is one of the most unique and most pristine environments in the world," said Reddy. Roughly ten percent of the world's penguins live on the South Sandwich Islands and many marine mammals inhabit the surrounding waters.

"I’ve never swam in such an area with so much wildlife," Pugh remarked. He and his team were unsure how the animals would react. Many have never come into contact with people. And they hoped the animals would not feel provoked.

"There’s nothing more frightening than swimming past a beach with elephant and Antarctic fur seals. I was praying they would stay right there," said the swimmer.

It's not the first time Pugh has put his body on the line to bring attention to environmental causes. His method of activism has been branded "speedo diplomacy," and regularly raises awareness about issues facing the ocean. In 2014, he was named National Geographic's Adventurer of the Year.

Following his swim in South Georgia, he plans to travel to the U.K. to meet with the leaders in charge of protecting the region he describes as "the most beautiful I've ever seen."