I am thrilled that the theme for this year's World Wildlife Day is #LifeBelowWater, and I am honoured to be celebrating it with my kindred species, the penguin. I've never met a penguin I didn't like, and I've been mixing with penguins ever since my very first long-distance swim, from Robben Island to Cape Town. That same colony of African penguins that was there at the start of that swim is there today, although their numbers have plummeted. If you ever want to smile deep down inside, go for a walk with a penguin. Over the years and in my travels to Antarctica I met many more penguins, and many different types. Whether they were Chinstraps, Adélies, Emperors, Kings or Macaroni penguins, they charmed me, every single one. Penguins are just perfectly themselves

1. Why have you decided to use swimming as a tool to protect our oceans?

Don't box me into a 25m long pool lane please! Swimming is my favourite thing to do, and my favourite place to swim is in the ocean. I need the pull of the tides, and the mysteries of the deep waters beneath me. Being surrounded by sea life put me in awe of marine diversity, and sensitive to its fragility. I believe that we can only protect what we love. And I care very deeply about our oceans.

2. What is the most memorable experience you have had in the sea?

I am tempted to say close encounters with leopard seals and elephant seals in Antarctica -- they were certainly the most frightening! But I think the most memorable was watching turtles hatch on a beach on the coast of Oman, and knowing that if they made it into the water of the Arabian Sea, they would be in a Marine Protected Area that was teaming with life, while so much of the seas around it had been reduced to the ocean equivalent of empty deserts.

3. How have our oceans changed since you first swam to Robben Island?

I've been swimming for 32 years and in that time I've seen our oceans change completely. What has shocked me the most during recent swims in the English Channel was the lack of sea life. When I should have been shadowed by dolphins or sharks, instead I found myself swimming through plastic -- and jellyfish, which are one of the few marine creatures to benefit from global warming.

4. What is the greatest threat to our seas?

Our seas today face a triple whammy: global warming, plastic pollution and overfishing all combine together to create a perfect storm that has devastating implications on our oceans.

5. What can people do to help protect marine life?

Collectively we need to reduce our carbons emissions drastically to stop global warming – and the resultant acidification of our seas and oceans – in its tracks. Individually we need to take responsibility for the waste we generate. Every single use plastic bag that ends up in the ocean can be a death sentence for a turtle, seal or albatross. Reuse it, or better still, refuse it. And last but certainly not least, we need to urge governments to create and enforce proper Marine Protected Areas so that marine wildlife can recover. Oceans do bounce back. We just have to let them.