The 315-mile swim, roughly 507 kilometres, will take him from the river’s source in the Adirondack Mountains to where it meets the Atlantic Ocean in New York City, home to UN Headquarters.

Mr. Pugh headed for the Hudson on Wednesday and is set to start swimming on Sunday.  He expects to complete the journey shortly before 20 September, when nations will begin ratifying the high seas treaty, aimed at protecting biodiversity in international waters.

The UN’s 193 Member States adopted the landmark legally binding agreement in June, following nearly two decades of fierce negotiations.

Clean rivers, healthy planet

“If we want healthy oceans we also need healthy rivers — it’s that simple,” he said recently. “Clean rivers are essential in the fight for global sustainability; indeed, our very existence depends on fresh water, clean air, and a habitable planet.” 

An accomplished endurance swimmer, Mr. Pugh has braved some of the most challenging environments on Earth, including the Antarctic, the North Pole, the Red Sea, and the Himalayas. 

The United Kingdom native was also the first person to complete a long-distance swim in every ocean of the world. The Hudson River swim is expected to take four weeks, making it his longest. 

“I specifically chose the Hudson for this swim because of the environmental progress that’s been made on the iconic waterway in recent years,” he said.  “Much work is still required, but tangible improvements have been made, setting an example for restoring rivers around the world.” 

Rocks, rapids and waterfalls 

Mr. Pugh will make the swim unassisted, meaning that he will only be wearing a Speedo, cap and goggles.  In comparison, assisted swimmers use equipment such as a wetsuit, snorkel, gloves, flippers and hand paddles.

His journey of 315 miles will begin with small steps at the Hudson River’s source, Lake Tear of the Clouds, located high in the Adirondack Mountains in northern New York state. Along the way he will encounter dramatic topological shifts, powerful river currents, and potentially toxic sewage runoffs during heavy rains.

“The Hudson is truly majestic, but, like most rivers, it begins with a trickle in fairly rough terrain, so this swim will actually have to begin on foot to negotiate rocks and very dense vegetation,” he explained. 

“That terrain quickly evolves into white water rapids and waterfalls that demand respect, so my expedition team and I are studying every twist and turn of the river keenly.”

Strength, stamina, perseverance

Mr. Pugh said he will hike and run around any rapids which are unswimmable, and the plan is to swim an average of 10 miles, or 16 km per day, depending on conditions. 

He will also start the swim wearing UNEP’s logo, agency chief Inger Andersen wrote on Tuesday on the social media platform X, formerly known as Twitter.  Expressing pride, she wished him “strength, stamina and perseverance” for the weeks ahead.

Mr. Pugh, 53, worked as a maritime lawyer in London before becoming a full-time ocean advocate.  He was appointed UNEP’s first Patron of the Oceans in 2013.

“Refuse, sewage, chemical and plastic waste don’t just pollute rivers and harm the species that live in them; these contaminants are carried on to the sea where they do more damage,” Ms. Andersen said recently.

“Just as we must keep our own arteries unclogged for our health, we must keep the planet’s arteries unclogged for its health.”