The Long Swim has been full of surprises. Some had to do with swimming, and some had to do with the reason I'm swimming.

I knew from the start that this swim would be tough. Fifty days was more than twice what I had ever swum before. But I didn't know quite how hard it would be. 

I thought that when I got past Brighton, just being 'in sight' of the end would buoy me on to Dover and those white cliffs would draw me in with (sort of chalky) open arms. It didn't work quite like that. 

Instead, I just got more and more tired as the swim progressed. The cumulative toll of kilometres of strokes, combined with an injury and lack of sleep ... it's really put a strain on the whole thing.

It hasn't just been tough on me, but on the whole team. All the positioning and repositioning of the yacht really took it out of us. For the last few weeks we've been up at 4 am to get into position, then back at six pm, which is when we get connectivity and can start catching up with admin and emails and write up the blog. We're getting to bed at midnight, which means an average of 4 hours sleep per night!

And then, the Dungeness headland proved to be a formidable foe.

Not all the surprises have been nasty. One of the nicest has been how welcoming people have been along the way. In Penzance, Plymouth, Portsmouth, Brighton ... I've been amazed at how people I'd never met before suddenly became crucial to the mission. Among these are Terry Portman, who opened Plymouth's doors to us and was indefatigable with her good ideas and humour; Candice Davis, the physio with the magic touch who, despite health issues of her own, came to the boat every day to treat my shoulder; Craig Roberts, the AFC Bournemouth doctor who gave me crucial exercises to keep me in the water and get me to the end ... Just three of the many angels who have helped us along the way. 

There have been beacons of inspiration too. Like the community in Lyme bay that teamed up with an NGO to protect their marine environment; or the efforts by scientists in Portsmouth to save the last remnants of what used to be the biggest oyster bed in Britain; or the Plymouth family that galvanised their community to stand up to dumping in Whitsand Bay. They are all heroes.

Despite these valiant efforts, the situation for our seas and oceans is dire. I have been deeply shocked by how little wildlife I have seen over the last 50 days – besides far too many jellyfish, not just for my comfort level, but for the oceans, since these are an indicator species for the effects of climate change. 

The only other marine animals we've seen over 560 kilometres have been a few dolphins, one turtle which dived when I saw it, and a lone shark ... So there is absolutely no doubt in my mind that the big industrial fishing trawlers that suck up every living thing in their path are having a devastating impact on our marine environment.

Our seas are in crisis and real action is needed right now. 

Despite my deep fatigue, my real work begins now too. I need to drive our message home to the foreign office, to Defra, to DFID, to the ministry of education ... so many different departments need to work together to protect our oceans. 

The task is not small. We need to restore something that has been plundered for 300 years. But if we all get on board, every individual, every family, every school, every community, we can make it happen. 

The oceans are tough, but they are also forgiving.