Internal waters are lifelines for everything that lives on our planet, and all rivers eventually find their oceans.

Mount Everest, Nepal

2010 | 28°N 86°E
22 mins 51 sec

I had resolved never to do another cold-water swim, but the Himalayas changed my mind. Glaciers are not just ice: they are a water lifeline for over 2 billion people, and if they melt away as scientists predict, the Himalayas will become the earth’s next big battle ground.

My kilometre swim across Lake Pumori, at 5,200m on Mt Everest, would draw attention to this issue. I took twenty-eight yaks and a speedo up the mountain, but I hadn’t factored in the radical tactical shift I would need to complete the swim.

I discovered that swimming at speed was not going to work at high altitude. Instead of minimising my time in the icy water and getting through the distance as quickly as possible, I was going to have to slow down. (Easier said than done in 2°C water.) This swim taught me that just because something has worked in the past, that doesn’t mean it will necessarily work in the future. I hope the world’s leaders are listening.

Watch the TedTalk

World Winter Swimming Championships, Oulu, Finland

2006 | 65°N 25°E

Finland has the World Wife Carrying Championships, the World Air Guitar Championships, the World Mobile (phone) Throwing Championships … and the World Winter Swimming Championships, to which I was invited.

I arrived to minus 17°C and men with chainsaws cutting the top layer off the frozen Oulu River estuary to form a 25m temporary pool. There were swimmers from Finland, Sweden, Germany, Australia, Great Britain and Ireland. But I headed straight for the Russian cold-water swimmer Colonel Vladimir Lutov and challenged him to a 2km swim.

The press billed it as the Real Cold War, and the Colonel nominated two younger Russians to swim against me over 500m. I beat Alexander Brylin by 100m, and came in 150m ahead of Vladimir Nefatov (to be fair, both were swimming breaststroke). But the real victory was finding camaraderie: when we three got out of the pool we shared a huge bear hug. Alexander and I traded swimming caps, dropped our bravado, and became firm friends. After all, when you’re only wearing a swimming costume there is simply nowhere to hide any animosity.

Nigards Glacier Lake, Norway

2006 | 61°N 7°E
1200m: 23 mins 50 secs

We chose this site because it was the closest sea level, ice-cold water to London, where I was lving at the time. We hadn’t counted on access to the swim being blocked by almost a kilometre of ice.

American sports scientist Jonathan Dugas was conducting the most comprehensive scientific test ever on a human’s ability to withstand extreme cold. The first summer thaw was the perfect time to swim, since we could be certain that the water would be 0°C. But getting to that perfect open patch of turquoise water at the foot of the glacier presented a challenge.

With Major General Tim Toyne Sewell in charge, my team cut a 700m long channel for the support boat to rush me from the end of the swim to warmth and safety.

As I dived in, icy water rushed down my throat. My skin felt like it was on fire, and my head was pounding. I forced myself to breathe calmly. I had to swim 6 widths of the lake to set a new world record. After just one lap, the pain was excruciating.

The local schoolchildren, waving Norwegian flags and shouting “Heia Lewis! Heia!” from the shore, spurred me on.

With two laps to go my core temperature had dropped to 37.2°C. I could feel my stroke shortening as hypothermia set in. By the final lap, my arms felt like lead. I learned that day that it is preferable to swim the distance in one go, rather than breaking momentum by turning. Every time you turn you want to give up.

I reached the end of the swim, but I wasn’t out of danger. My body temperature plummeted to 33.6°C as the cold blood in my limbs returned to my core. I was intensely grateful for that channel, which helped get me to a warm shower.

Read The Ice Bear Cometh, Wearing Nothing but a Speedo from the NY Times.

River Thames, United Kingdom

2006 | 51°N 0°W
350kms: 21 days

When I dropped a stick into the water at the source of the Thames to test its flow, I couldn’t imagine that it would be dry seven weeks later. But when I arrived to begin my 350km swim of the River Thames from source to sea, there was no water whatsoever. I had to run 40kms in blistering heat before I found enough water to swim in.

I thought it would take 10 days to reach the North Sea. It took twenty-one. I should have planned better. It was the worst drought in living memory, and the river was sluggish and often polluted. I got sick, repeatedly. The supporters along the way were amazing, but in London the harbourmaster wanted to throw me in jail. Still, the Prime Minister invited me to Number 10 to discuss the country’s carbon emissions, and the UK enacted the Climate Change Act soon afterwards.

Lake Malawi, Malawi

1992 | 11°S 34°E
25km: 9 hrs 52 mins

When people think ‘most dangerous animal in Africa’ they usually think lion or leopard or snake. But it’s actually hippos and crocodiles. Hippos kill more people each year than any animal (after mosquitoes), and Lake Malawi has plenty of them.

They were all I was thinking about for the first 200m of this swim. I just wanted to get out into the safety of the deep water, so I kept my head down and focussed on speed. I didn’t even take a breath, let alone look where I was going.

Until I heard a shout from the support boat: my right arm is much stronger than my left, so I had swum a full circle and was still splashing around in the shallows! The pilot of the boat must have thought I was crazy…

The local people certainly did. No one had ever tried to swim across the lake before. We made it – but our equipment didn’t. The night before the swim all our gear was stolen – including sunscreen. Luckily I’d slept in my swimming costume, but I got really badly burned. Now I keep my essential swimming equipment with me at all times.

Spin the Globe

Explore the world and see where Lewis has swum. Click on any pin to find out more about that particular swim.

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