Evening is falling and the cold winter light is bleeding out of a steel-coloured sky. Soon the short Scandinavian afternoon will give way to night here on the edge of Lake Sonnanen in the south of Finland. Not a single gust of wind moves the pine branches; not a single ripple disturbs the water’s surface. Nothing disturbs this infinite expanse of trees, ice and snow enveloped by absolute silence.

It’s here, in a simple hunter’s lodge 170km northeast of Helsinki, that freediver Johanna Nordblad and her sister and personal photographer, Elina, spend most of their free time. With urban rhythms left far behind, their days are occupied by shovelling snow, gathering firewood and spending long hours after dinner chatting by candlelight.

“Elina and I always come up here whenever we can. I love this natural setting, these lakes,” explains Nordblad. “People don’t like to practise freediving in Finland because the water is black in the depths, but that’s exactly why I like it so much. Down below there are no colours, no sounds. There’s nothing… You are completely alone with yourself.”

‘I love this natural setting, these lakes’: Nordblad getting ready to dive under the ice. Photograph: Elina Manninen/The Observer

Nordblad, 44, from Finland, first freedived in 1999 after years as a scuba diver. The feeling of lightness proved liberating, and being able to swim without the weight of equipment won her over instantly. She began competing at world championship level – taking part in events where divers perform in different disciplines to see who can dive the deepest, or stay underwater the longest, with no breathing apparatus. There are 11 types of freediving – for example, diving for depth or swimming horizontally, with or without weights, with or without fins, in open water or swimming pools. Nordblad specialises in dynamic freediving with fins, which involves swimming as far as possible horizontally underwater on one breath.

In 2004, in Cyprus, she set the women’s world record by swimming a horizontal distance of 158m, and since then she has ranked among the best freedivers in the world.

“The most difficult thing is watching the seconds go by. After two or three minutes your mind starts listing all the reasons why you should go back up to the surface instead of staying underwater. The more time goes by, the harder it gets. You need a lot of self-control,” she says.

But then, in 2010, a serious accident changed her life and set her on the path to make her mark in a new discipline, one in which she still holds the current world record: freediving under ice.

“I was riding a downhill bike, travelling a slippery, muddy path down a hill when suddenly I began to slip,” she recounts. “The fall wasn’t particularly dangerous, but I was unlucky and I hit a rock. My left leg was smashed into a thousand pieces, like a twisted branch.” Rushed to hospital, Nordblad underwent delicate surgery. The swelling and compound fractures were so serious that the doctors weren’t able to sew the leg back up and close the wounds until another 10 days had passed.

A graphic designer by trade, she decided to sell her agency in Helsinki and say goodbye to the 13 people who were working for her to concentrate on rehabilitation, a painful and complex process that lasted for more than 18 months, consuming all her energies.

‘My leg smashed into a thousand pieces’: Nordblad on the bicycle accident that sparked her diving career. Photograph: Elina Manninen/The Observer

After another year had passed she was finally able to walk without a stick, but the nerves in her leg were so badly damaged that the pain was profound and persistent. “That’s when my doctor recommended I try cold-water therapy,” says Nordblad. “The first time I put my leg in 4C water I only managed to keep it in for a minute, but the relief was immediate. Finally, it didn’t hurt any more.”

As the months passed, Nordblad became so accustomed to the cold that she found she could no longer do without it. She began immersing the other leg as well, then her entire body, ultimately even her head. “I liked the way it felt. That’s when I first got the idea of diving beneath the ice. What better place to try it than Finland?”

In what is known as apnea – conducted beneath the ice – the diver has to move horizontally, covering a preset distance between two holes cut into the ice. In 2015, Nordblad set the women’s world record in this discipline – 50m – wearing only a simple swimsuit and goggles. The water temperature was barely 2C. “Up until the end I was afraid that my head, the part of the body that suffers the most during low-temperature dives, couldn’t take it,” she confesses. “But in reality things were easier than I’d anticipated.”

While her sister is preparing dinner, Nordblad sits on the little wooden dock that runs out from the bank into the lake, busy breaking up the thin layer of ice that’s formed on the water’s surface over the past couple of days. After she’s pushed a few sections underwater, she lights a series of candles that illuminate the wooden stairs leading down into the water. Soon she’ll be able to take the first dive of the season. She’s been waiting for this moment for weeks, and it stirs emotions she finds hard to conceal.

“I love diving, feeling the water run between your fingers… When you’re down below there’s no margin for error. You have only yourself to trust. You have to be relaxed and in control at the same time,” she explains. “Freediving requires physical effort, but mental discipline is even more important. You have to do the dive without panicking or losing your head.”

Swimming beneath ice has other pitfalls. Visibility is one, since the thick layer of ice and snow on the water’s surface often reduces vision to a minimum. It’s easy to become disoriented and not be able to even see the exit hole, so much so that safety ropes are extended between the holes. “Sometimes I can’t even make out my own hands. That’s how dark the water can be. In the event of a real emergency, my safety plan is to swim down deeper below the surface. That’s the only way I can look up and see light coming in from the two holes and figure out where I can get out.”

Although it’s hard to believe, Nordblad is afraid of the depths. Every time she goes freediving and swims down to the Finnish lakebed, her mind turns to sea monsters and unknown creatures that populate the abyss. “The deepest point I reach corresponds to the extreme limits of my ability to dominate my fears. Otherwise I could go much deeper,” she says with a smile.

Although she still holds the record for diving beneath the ice, for Nordblad freediving has long since evolved into something more than a desire to beat her opponents. “If you compete with that mentality, you’re not enjoying the moment. I don’t deny I thought that way when I was younger, but now I don’t like it any more.

‘So many windows of opportunity open up around you’: Nordblad on winning. Photograph: Elina Manninen/The Observer

“When you win, the expectations of those around you increase automatically,” she says. “So many different windows of opportunity open up around you that you have to be good at figuring out what you want from life and what you truly desire from this sport.”

In 2006, Nordblad earned one of just three government grants reserved for non-Olympic Finnish athletes. Not by chance, that was the year she found herself training the least. “Going to the pool just wasn’t fun any more. I was losing motivation. I love apnea because I find it more stimulating than spending hours looking at a computer screen, but I realised I was turning it into a job just like any other,” she explains. “One of the most beautiful periods of my life was the time just after my rehabilitation. I spent two years out in the open: I would take my kayak and go out and explore the islands around Helsinki. There are hundreds of them, and all you need is to paddle for five minutes before you’re completely lost in nature.”

At the end of the month Nordblad will attempt to beat the men’s ice freediving world record (currently standing at 76.2m and held by Stig Severinsen, a Danish four-time world freediving champion). She is aiming to swim horizontally beneath the ice for 81m. She will take the challenge in her stride, almost as if it were a game. Sometimes that’s how remarkable achievements are accomplished.