Wild swimming

哈利刘易斯and James Tytko prepare for a dip in the River Cam, Cambridge. Down a quiet strip for the river, trees overhang the water and the occasional punter drifts downstream. They are joined by Simon Crowhurst, Nicky Blanning and Alex Buxton...

Harry - That was quite impressive, James. Are you gonna take the stairs?

James - The slow way in?

Harry - I think there was really quite a stark difference between the way you got in, James, compared to Nicky, Alex, and Simon.

James - Definitely. How long until I acclimatise?

Simon - well, you need to move, give it a minute.

James - Okay. I'm good.

Harry - You're listening to The Naked Scientists and it's our summer special. So that's with me, Harry Lewis, and I've managed to drag James Tytko out the office too. Is it a hot one where you are at the moment? Because it certainly feels like it has been here over the past few days and, to beat the heat before the show kicks off properly. It looks like James and I are gonna get lured in for a wild dip in the river cam in Cambridge.James and I are joined by Nicky Blanning, gliding effortlessly through the water alongside Alex Baxton, and here on the banks with me is Simon Crowhurst. Coming down on such a beautiful day, where are we and what are we looking at?

Simon - We're on Sheep's Green. We're looking at the river Cam banked with beautiful willows. So I can see my wife and my friend, Nick, in the water swimming along and enjoying the water, which at 21 degrees is warmer than it usually is during the year. Wild swimming has increased in popularity immensely over the last few years and we've got so many applicants to join our swimming club that we can't cope with the numbers.

Harry - And you said it was 21 degrees, which sounds actually quite warm. I'm quaking in my boots about getting in Simon, because I hate the cold, but 21? How can you prove that that's 21 degrees? Well,Simon We've got a thermometer in there so we can take a look at the actual measurement. Let's do that.

Simon - So here we are with an old fashioned analog thermometer. We'll take it quickly to the water before it has chance to change. It's just under 21 degrees and you can see the liquid falling immediately as it comes out of the water because it's cooling down in the air, working a bit like a fridge.

Harry - James, you just jumped out of the water as well. A valiant effort, I thought, when you got in. How was it?

James - Yeah, it's definitely a cliche but it's lovely once you're in.

Harry - Simon, you said that at the moment your particular swimming club's literally just got too many applicants to be able to support. Do you think that's representative of the rest of the rivers and wild swimming clubs around the UK?

Simon - Well, there's been a tremendous surge in interest and activity of wild swimming. As long as people do it safely and responsibly. I don't think it's a problem. Where people just charge into the water without any experience -without being strong swimmers - then you can have problems and people can get into difficulty very quickly.

Harry - Nicky and Alex you've swam over to us graciously, I might add. There wasn't quite the calamity of when James got in and he was holding his breath as hard as possible. What's it like? How's the river?

Nicky - Oh, it's really beautiful. Honestly, it's absolutely gorgeous. I could stay at it for hours.

Harry - Well, I know for a fact, Nicky, you've actually been out twice today. Now you were up this morning, weren't you?

尼基-我,是的。我在丽都,我试着游nd swim twice a day at the moment in the summer while it's so nice.

Harry - I mean, there are health benefits that are supposedly associated with getting yourself in cold water. Obviously ,exercise is good. You're in nature, so it's a little perk for your mental health, isn't it? Are these things you think about or is it just the fact that, you know, I've got a bit of extra energy and I'm up nice and early. Why not get out there and into the world?

Alex - It becomes an addiction. I think Nicky would probably agree with this, an addiction. It's like your daily fix of something that's you know, it's a good addiction to have, I hasten to add.

Simon - It's one that has a positive effect on your physical and your mental health. I find it punctuates the day really well when I've been for a swim, it almost doubles the enjoyment that you get out of the day

Harry - On a day like today, it makes complete sense to make use of it, seeing as it's on the doorstep. Are you guys coming out here when it's not warm and sunny, when it's not 21 degrees in the river?

Nicky - Yes. I think the coldest I've swam has been actually when the river's been frozen and I've cut a circle in the ice and swam round in a circle.

Harry - You can't see it, but I'm astonished. Nicky, was this witnessed by anybody?

Nicky - Yes I have photographs.

Alex - We waded through snow to get to the river and you can't even see the edge of it

Nicky - We waded through floods of water!

Alex - That's what I mean by an addiction.

Harry - And as well, this is based on swimming that's been done here historically. Isn't it? There's photos of this exact area. Taken en mass.

Alex - Before indoor pools were built, before that, everybody swam in the river. My mother was brought up in Cambridge and she learned to swim in the side river here in the 1930s. You had to swim as a child. You had to show you could swim in the shallow side river before you were allowed in the main river, and there were people actually in charge of all this.

Harry - Well, that's probably changed quite a lot today. There isn't really a body or governing body that does look after swimmers in wild rivers is there? And Imean, that brings me onto, I guess, a more general question. It's not quite the picturesque clear colorless water of the Maldives. There is a dark kind of murky green isn't it, the river Cam? . So do you feel safe when you get in and out? Is there any worry about the cleanliness of the water?

Simon - Yes. There are concerns about the water quality and we are downstream of water treatment plants. The water quality does vary. There are people who heroically monitor the water quality through the year. We know there are times when the bacterial load is higher. Some of that is due to release from sewage works. Some of that is due to more suspension of particles in the water when the river flow is higher and it's hard to separate out those two effects.

Harry - And how do you feel, Nicky? Is there any fear when you get in or...

Nicky - I certainly think about it more when it's flooded and there's been heavy rainfall. I think you have to be more sensible then and I tend to keep my head out of the water. It doesn't stop me swimming, but I do think about that.

Harry - Right. Well saying that I think I put it off long enough now. I better get in as well.

Harry - Go on then. Before I dip my toe in the water, let me catch you up to speed. So, the plan is that we are going on a river trip down the river Cam right into the heart of Cambridge. We'll be stopping at sites of scientific importance on the way. So hopefully we'll also get a chance to leaf through a couple of history books, too. Sport, wildlife technology, all to come. But first we better meet captain Peter, which we'll do straight after this. God, it's gonna be so cold.

James - Don't build it up. Okay.