Marathon swimmer Lewis Pugh has completed a 507km swim down the United States’ Hudson River, a month-long endurance test designed to shine a spotlight on the world’s rivers and the benefits of cleaning up long-neglected waterways.

Pugh, a United Nations Environment Programme (UNEP) Patron of the Oceans, arrived on Manhattan’s southern tip on a crisp September morning, exhausted but jubilant.

“Fifty years ago, a swim like this would have been absolutely impossible. This was once one of the most polluted rivers in the whole world,” said Pugh on his arrival.

He noted that decades of cleanup efforts have helped revive the Hudson, a push that comes as many other rivers across the planet face mounting pressure from pollution, climate change and over-extraction.

“I pray that [people around the world] are going to be inspired by what happened here and say to themselves ‘If they can do that in the Hudson, surely we can do that in our river’,” he said.