I was swimming off Plymouth, my home city, this morning and the waters have changed since I was a boy growing up here.

I learned to swim with my parents off the beautiful golden beach of Whitsand Bay. When I was young there would be no plastic there. Now, you find plastic coming in with the Atlantic Ocean.

It's happening all the way along our coastline. The birds are eating the plastic, as are the fish.

The impact on our oceans is devastating.

I started today's swim with the support of 60 members of Devon and Cornwall Wild Swimming club.

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All kitted out in Speedo's, we jumped in the sea at Tinside Beach and swum together out to our Princess speedboat, which was whisking me to today's start point.

The Wild Swimming club sent two of their finest along with us, who joined me for much of the swim.

They acted as my good luck charm as today was the very first day that I've not been stung by jellyfish - we still had to dive out of the way of a few large compass jellies though!

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Jellyfish are an important indicator species - they bloom in warm waters and we are now seeing unprecedented numbers.

The fact that I've been seeing (and have been stung) by so many on my swim so far is a painful and poignant reminder that our waters are already feeling the effects of climate change.

We need to wake up and take strong action before it's too late.

After today's morning swim, I opened an exhibition about marine conservation and plastics in the ocean.

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4.3 miles (6.85km)