An endurance swimmer and United Nations oceans advocate is on a quest to swim the length of the USA’s iconic Hudson River to draw attention to the critical importance of healthy river ecosystems.

Lewis Pugh is the UN Environment Programme’s (UNEP) patron of the oceans. He has embarked on a 507km (315 mile) swim, taking him from the river’s source in the Adirondack Mountains in New York state, to where it meets the Atlantic Ocean in New York City, home to UN headquarters.

Lewis set off in mid-August and expects to complete the journey shortly before 20 September 2023, when nations will begin ratifying the high seas treaty, aimed at protecting biodiversity in international waters. The UN’s 193 member states adopted the legally binding agreement in June, following nearly two decades of fierce negotiations.

Pugh said, “If we want healthy oceans we also need healthy rivers — it’s that simple. Clean rivers are essential in the fight for global sustainability.

"Indeed, our very existence depends on fresh water, clean air and a habitable planet.”

Lewis worked as a maritime lawyer in London before becoming a full-time ocean advocate and founding the Lewis Pugh Foundation, which aims to take meaningful action to properly protect oceans.

He has braved some of the most challenging environments on earth, including the Antarctic, the North Pole, the Red Sea, and the Himalayas, and is the first person to complete a long-distance swim in every ocean of the world. He was appointed UNEP’s first patron of the oceans in 2013.

“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.”

Lewis will make the swim unassisted, meaning that he will only be wearing trunks, cap and goggles. His 500km-plus journey began 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.”

Lewis will hike and run around any rapids which are unswimmable and plans to swim an average of 16km (10 miles) per day, depending on conditions.