I hear a faint sound and then a loud noise hits me and makes my legs vibrate. It sounds like someone playing a triangle over and over. As I keep swimming along underwater, the sound - booming out of a small blue speaker at the foot of the pool - grows and envelops me. It's astonishingly immediate, inescapable, and faintly perplexing.

Treading water a few lanes across from me here in London Fields lido is Joel Cahen, topless and sporting a pair of pale trunks. The 35-year-old sound engineer and artist has spent the last year co-running Scrap Club, a sporadic event that invites people to abandoned warehouses to cathartically demolish old fridges, computers and even cars. Now he is curating the UK's first "underwater sound festival". Called Wet Sounds, it launches this Sunday in east London before touring, giving swimmers up and down the country an underwater blast for no more than their pool admission fee. I'm here on a bright Friday morning for a sneak preview.

So how did this all come about? "I just became fascinated with swimming pools," says Cahen. "They offer a unique way to listen to sound art. I'm interested in the way the audience perceive it, as they float along or dive in." Wet Sounds began as an idea in February 2007, when Cahen was swimming three times a week. One day, after a couple of lengths, he had lunch with a friend who said she had been to a pool abroad that had underwater speakers. Cahen was amazed. "I was like: let's try and do that here," he says. "I decided to come up with a gallery of sound art to be experienced in a pool."

After securing funding, Cahen asked artists to send him appropriate sounds. He received hundreds of responses from all over the world. These were whittled down to two hours of sound. "In the end, I got mostly water sounds," he says, although Chris Watson, a sound recordist who has worked for David Attenborough and was in Cabaret Voltaire in the 1970s, submitted recordings of sea life made with hydrophones - microphones that detect sound under water.

We are not alone in the pool. The beaming sun has attracted early risers keen to get a few lengths in before work. As Cahen hits play, the other swimmers glance over, but say nothing - except for one guy who can't contain himself. "This is brilliant," he says. "I'm going to bring my son along."

I submerge my head and swim down to inspect the speakers. They are hooked up to Cahen's dusty black iPod, which is resting on a plastic table poolside. A track blasts out at me, an upbeat mix of funky, clashing electronic noise that changes into an eerie, hypnotic rhythm. It's a bizarre experience, a bit otherworldly. I swim away from the speakers to see if the track can be heard from a distance. It can. The sounds are pulsating through the water at speed: sound travels up to four times faster in water. With my whole body immersed, it feels as if they're hitting every limb. It's not like listening to music in the bath, with your head under the water: there the music gets distorted. What I'm listening to is razor sharp.

I come up for air and look around at the swimmers' heads going up and down in time with their arms. No one stops to take in this fairly unusual event - sound pumping up from the bottom of their pool on a Friday morning. Then, all of a sudden, there's silence. Perhaps there's a technical hitch. I see Cahen jump out of the water, dripping wet. As he inspects his equipment, it starts to dawn on me how dangerous it is to mix sound, electricity and water. Is he worried? "The speakers are marine speakers, designed to go underwater, and they're connected to the amp, not directly to the electricity. Everything has been tested, so I'm not worried. The first time I ever tested this out, I jumped in, and only when I was in the water did I stop and think. But by that point I was OK, I hadn't suffered any shocks."

If the tour is a success, Cahen wants to have a permanent Wet Sounds exhibition. "I'd love to take on Haggerston Pool [a Hackney venue that has been closed since 2000]. I'd use Wet Sounds to bring back interest in the pool. People could go in and listen to sound art. There'd be the wall lights, installations and other stuff ..." His voice trails off and then he's gone, back down to hear the booming below.

· Wet Sounds launches on Sunday at London Fields lido, London. Tour details: newtoy.org