CNN  — 

Fifty-year-old Lewis Pugh says he was terrified when he plunged into the water of East Antarctica in nothing but swim briefs, a swim cap and goggles. He was even more terrified when he swam below the Antarctic ice sheet, through melting tunnels – though he said it was the most beautiful swim he’s ever done.

Pugh is known for swimming in Arctic water to raise awareness for climate change, but on January 23, he became the first person to swim in a supraglacial lake – a lake that has formed on top of a glacier because of melting ice.

“(The swim) was terrifying for a number of reasons,” Pugh told CNN. “First, the water is so cold for a swimmer. It was 0 degrees centigrade, just above freezing. But also, it illustrates very very graphically what is happening in East Antarctica.”

The point he was trying to make, he said, is that it shouldn’t be possible to do the swim, but it is because of cracks in the glacier.

Pugh said he was motivated by a September 2019 study in the journal Scientific Reports that discovered more than 65,000 supraglacial lakes on East Antarctica’s ice sheet.

The study explains that supraglacial water is concerning because it can pour into cracks, fracturing glaciers and speeding up glacier melting and sea level rise.

This alarms Pugh, who says climate change is already moving rapidly. He says he wants immediate action at this November’s climate change negotiations in Glasgow, Scotland, which is why he chose to go swimming in an area that he calls “the front line of climate change.”

“I’m saying to world leaders please, come to Glasgow, come there with a lot of ambition,” Pugh said, “Step up, or step aside, because we simply don’t have any more time on our hands.”

Pugh recently took his message to the Kremlin, where he attempted to persuade the Russian government to establish a marine protected area in East Antarctica to protect it from overfishing. Pugh says international law requires a specific group of 25 nations to agree, and all but members Russia and China have signed on.

He says he is hopeful that Russia will agree to this deal later in the year.

“We’ve got to move away from the talking, and now start taking the action,” the activist said.

“We were positively received and I’m quietly hopeful that at the end of the year when we come to the negotiations to try and create this protected area in this region, I’m quietly confident that Russia will now agree (to) this deal,” he said.

Several years ago, he negotiated with the Russian government in an attempt to create a marine protected area in another part of Antarctica, the Ross Sea. That area became a marine preserve in 2016.