Today we set sail from Dartmouth, which has been our home port for the past week, headed for the middle of Lyme Bay.

We plan to spend the next 36 hours at sea, doing an afternoon and a night swim today, drifting out to sea overnight, and then one more swim tomorrow afternoon.

We will be 50km out to sea, which will be too far for us to motor back to a port for the night.

On the journey out, we were once again joined by a small pod of dolphins who swam close alongside us, splashing and clicking. Their grace and agility spurred me on, welcoming us to Dorset as we crossed over the county line from Devon.

Conditions were perfect - after days of rough seas, rain and high winds, today the ocean was finally calm and inviting. There was no swell, no wind, no cloud. Just 180⁰ of beautifully flat water, joined at the horizon by 180⁰ of clear blue sky.

My midday swim was the fastest swim I've done yet, even quicker than yesterday. I covered 10km in under two hours helped by the strength of the current behind me.

Whilst we no longer have the full force of the spring tides with us, we aren't quite into the stagnation of neaps yet, so the added boost of a knot and a half of current propelling me forward was both literally and emotionally uplifting.

After two hours and one minute, I got out to a welcome lunch of jacket potatoes covered in sea salt, melted butter, cheese and mayonnaise. Sometimes only comfort food will do to celebrate a success - the athlete's diet be damned.

The plan was to spend the next 10 hours drifting with the engines off, so that we could pick up the same current at midnight and eek out the last of the added lift from the current.

We set up three hour shifts to keep an eye on our position and any other (non-existent) ocean traffic. There was no phone signal or internet and no electricity - just eight people bobbing about in the middle of the English Channel with nothing to do and time to while away.

For the first time, the eccentricities brought on by cabin fever became apparent. There were mass exercise classes led by my trainer, Nicola, along with shoulder massages for whoever was at the helm. There were trips up the mast.

There was the first Nail Clipping Distance Championships - I will not say who took part, or who won. There were many, many games of Uno with increasingly outrageous forfeits. Members of the crew found themselves having to do laps of the boat in increasingly bizarre swimwear.

As the sun finally bled away into the horizon, tiredness began to pull at us all - we had been up since before 6am and had many hours still to go. Even Uno began to get a little repetitive.

After ten hours of patience, it was finally time for the midnight swim. The current was even stronger than it had been this morning - I had a real chance to get ahead of schedule here and put an extra 10km behind me.

As before, I put glow sticks around my wrists and under my swimming cap so that the crew could find me in the dark.

They pulled out powerful torches to light my way, and switched them onto the water just as I was about to dive in.

To our collective horror, what the light revealed was the densest bloom of jellyfish I have ever seen in my 30 years of swimming.

It was endless in every direction. Not just the relatively harmless moon jellyfish we saw near Land's End, but species we had never seen before, but which hardly looked like pacifists.

They were monstrous - thousands had bulbous heads larger than mine and were more than 2m long with their frothy tentacles trailing horizontally in the current.

There was no way to find a clear path through, it was unswimmable without a wetsuit for protection. To swim by Channel Swimming Association rules, I could only wear my Speedo swimming trunks, a cap and goggles. There would be nothing to guard against their stings.

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I was agonizingly torn. I had brought my crew 50km out to sea, they were sleep deprived and were on harsh water rations. After the sun had set, it got cold and they were groggily wrapped up in jumpers and woolly hats - and now I couldn't swim.

I simply couldn't do it to them. I decided we would wait another quarter of an hour to see if the bloom ended so that I could swim. The tension grew as the minutes ticked by. No fewer jellyfish.

Skipper and I had a hushed conversation on what I should do. Five stings, we decided. Any more than that and he would pull me out. Nicola would be at the ready with a bottle of vinegar on my exit.

Looking into the blackness of the sky above, I whispered a few words in the hope that someone might be listening, and dived in.

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Immediately, I was hit. Again and again, they covered my body. This was lunacy. It was like taking a shortcut across a minefield. The progress I'd make in terms of distance from the strong current tonight would be lost tenfold tomorrow if my body was covered in stings.

I lasted eight minutes before crawling up the ladder and falling onto the stern. I didn't even count the stings. I berated myself, even though I knew deep down there was nothing I could have done to predict this.

Still livid, I crawled into bed, weary from the physical and mental strain.

My crew took it in turns to keep watch over Aquila all night long, none of them sleeping more than two hours undisturbed.

This is the ugly reality of climate change on our English Channel, thousands and thousands of jellyfish streaming through our waters unchallenged by other species. My crew and I bore witness to it, my body bearing its marks.

And it outraged us.

11.26km (7 miles)