Lewis William Gordon Pugh, OIG, (born 5 December 1969) is a British-South African endurance swimmer and ocean advocate. Dubbed the "Sir Edmund Hillary of swimming", he is the first person to complete a long-distance swim in every ocean of the world, and he frequently swims in vulnerable ecosystems to draw attention to their plight.

Pugh is known for undertaking the first swim across the North Pole in 2007 with the aim of highlighting the melting of the Arctic sea ice. In 2010 he swam across a glacial lake on Mount Everest, to draw attention to the melting of the glaciers in the Himalayas and the impact the reduced water supply would have on peace in the region. In 2018 he swam the full length of the English Channel to call for 30% of the world's oceans to be protected by 2030.

Pugh was named a Young Global Leader by the World Economic Forum in 2010 and the United Nations appointed him as the first UN Patron of the Oceans in 2013.

In 2016 Pugh played a role in creating the largest marine reserve in the world in the Ross Sea off Antarctica. The media coined the term "Speedo Diplomacy" to describe his efforts of swimming in the icy waters of Antarctica and shuttling between the US and Russia to help negotiate the final agreement on the reserve.

Pugh currently serves as an Adjunct Professor of International Law at the University of Cape Town.