Kiyoshi Miyasaka climbs the stone steps of his shrine, autumn leaves crunching under his feet. The Shinto priest, dressed in white, aims an orange leaf blower at a row of cobblestones and clears the path of fallen leaves.

“I know people would rather see a lone priest sweeping up with his broom,” he says. “But we’re a bit more modern than that, and frankly, I can’t get to all the leaves otherwise.”

It is an unseasonably warm November morning. The trees only changed shades a few weeks ago, and the steep hill behind the shrine looks as though it’s on fire. The 69-year-old eventually puts down the roaring machine and sweeps up the lingering leaves into neat piles. Then he changes into formal robes to offer a tray of rice, sake, salt and water at the shrine’s altar, and begins his prayers.

Below him, Lake Suwa looks like frosted glass, the surface mimicking ice so fragile it may crack at any moment. But the lake is far from frozen.

For nearly 600 years, priests at Yatsurugi Shrine have observed ice cover on the lake here in the Japan Alps, diligently recording it by hand and storing it safely, first in the shrine’s vault and later in a local museum. These records represent one of the world’s oldest continuous measurements of climate change, written long before the priests knew what they were providing.

Miyasaka is the fourth generation of his family to watch over the lake as priests, keeping track of a phenomenon they call omiwatari, or the crossing of the gods.

For omiwatari to form, the lake needs to freeze over completely and air temperatures have to stay below minus 10 C (14 F) for several days in a row before warming ever so slightly. Then, with what at first sounds like distant drums, giant sheets of ice crack and buckle over each other into a miniature mountain range.

At first villagers feared the roaring sound of the crashing ice and imagined the ridge was the scaly back of a dragon living in the lake’s watery depths.

“Do you know what the foundation for religion is?” asks Miyasaka, speaking as if he’s addressing a room full of students. “Fear of nature. Then comes appreciation, then familiarity, and then we take it for granted.”

With global temperatures steadily rising in recent years, Lake Suwa rarely freezes solid, even in the coldest months of the year. The ice, once so thick that army tanks could rumble over it, is often too thin now for the mythic omiwatari to appear.

And the lake, once so central to the town’s identity, is slowly vanishing from the everyday lives of the people who surround it. As winter nears, Lake Suwa provides an intimate reminder of the damage wrought by climate change — and its ability to erase the very things people hold most dear.

During the entirety of the 17th century, there was only one year without a sighting of the omiwatari. Between the end of World War II and 1988, the ice ridge failed to form 13 times. Since then, the omiwatari has become rarer still. The crossing finally appeared last year after a four-year absence.

Miyasaka flips through a folder filled with newspaper clippings and photographs of the lake. In one laminated black-and-white picture, local firemen pose in front of a fighter plane that landed on the lake ice during a military exercise before the war. In a more recent photograph, Miyasaka and a group of local leaders stand precariously on the lake to examine an ice fracture beneath their gumboots.

“You could say the gods aren’t hearing my prayers,” he says, softening his words with a smile.

A childhood on the lake

It’s a little past 10 a.m. by the time Atsushi Momose finishes his coffee in his garden. He stubs out a hand-rolled cigarette in an ashtray and grabs a life jacket off the ground. It’s Sunday, but he still has to complete his daily routine of cleaning the lake he’s loved since he was a child.

Momose removes a tarpaulin covering his kayak. He moves his hand over the gleaming wooden vessel, which he built using a plan he ordered online. He hoists the kayak onto a trolley and rolls it onto a side street.

“These all used to be small inns and houses,” he says as he passes by parking lots. A 14-story hotel blocks Momose’s view of the lake from his childhood home, where he returned to care for his elderly father after retirement.

When he was a boy, a popular teenage movie star visited the lake wearing a figure skater’s costume and expensive leather skates.

“I remember a bunch of us boys hanging around on the ice, trying to talk to her and then suddenly, she slipped and grabbed my arm for support,” the 71-year-old says. “My heart stopped. I still remember it.”

With the help of a friend, Momose hauls his kayak into the lake and slowly lowers himself in. It sinks under his weight, but he quickly regains balance and paddles out onto the water.

When Momose first returned to Suwa after a lifetime bouncing from one city to the next working as a documentary filmmaker, he was surprised to find the lake deserted. Plastic bottles and cigarette butts littered the water’s edge. In winter, police and tourism organizations put up ugly red flags all around the lake to warn residents and tourists to stay away from the ice.

These days, Momose starts most mornings on the lake, picking up floating debris using long silver tongs.

“Nobody even looks at the lake anymore,” he says as he braces his feet inside the kayak and floats in place. Murky water laps the sides of the boat. “I think we should try and give back to this place since it gave us so much.”

Momose’s paddle creates ripples in waters that are eerily quiet for a weekend morning. The only noise comes from a pair of children furiously pedaling a swan boat, waving and calling out to parents watching anxiously from a nearby pier.

Shinto priest Kiyoshi Miyasaka displays a photo he took on Jan. 13, 2006, that shows a phenomenon called omiwatari (the crossing of the gods), which occurs when Lake Suwa freezes over and two sheets of ice collide to create a ridge across the surface. | REUTERS

Ignored warnings

Rusted fishing boats are still anchored near the pier. Kanji Fujimori, 75, who recently retired as the head of the local fisheries union, walks up the stairs of a local community center in his socks and sits at a large desk in the building’s empty library.

Though he has retired, Fujimori still spends most of his days deep in research. He recently self-published two tell-all books about his tenure at the union, which had fallen into mismanagement and debt when he took over. In them, government bureaucrats with barely veiled pseudonyms refuse to listen to his warnings and fail to take aggressive measures to clean up the lake.

“I’ve been saying for years that the level of oxygen in that lake is dangerously low,” he says. The community center’s only staffer looks over at Fujimori, then returns to his computer.

“No one listened to me or believed me.”

Then in July 2016, Fujimori got a call from a veteran fisherman that mounds of dead fish had washed up on the lake’s shores overnight. He spent the rest of the day fielding calls from residents all around the lake with more sightings of dying fish. The “mass death” event, as he calls it, was so shocking it made it into national newspapers the next day.

The Suwa fisheries union estimated that around 80 percent of the smelt in the lake washed up that day. A Nagano prefectural fisheries lab published a similar estimate. After the die-off, the prefecture created a task force of local professors and experts to study the lake.

Up until the 1940s, the union regularly handled 1,000 tons of catch, mostly carp and smelt, a year. This has now dwindled to 10 tons, barely enough to supply local restaurants and hotels. The loss of ice in winter also means that traveling water birds can feast on fish year round. Because the birds are protected in Suwa and can’t be shot, frustrated fishermen have resorted to chasing the birds with speedboats and using air horns to scare them away.

These days, there are only a few dozen fishermen on the lake, Fujimori says.

An alley behind the community center opens up to a scenic lakeside road, where an imposing mansion stands as one of the few reminders of Suwa’s gilded past.

When Japan opened up to trade with the rest of the world in the late 19th century, raw silk made up the majority of the country’s exports. Thousands of girls from neighboring villages were sent by their families to Suwa, where they lived in cramped dormitories and spent long, grueling hours working in silk mills. In its heyday, the mills around Suwa manufactured the bulk of raw silk produced in Japan, and the area is still considered by some to be the birthplace of the country’s industrial revolution.

The mansion was built in the 1920s by a wealthy resident nicknamed the “silk emperor” as a place where working women from nearby mills could rest and recuperate. The emperor’s silk mills are long gone, but visitors still come to the mansion to see the gigantic Roman bath inside, large enough to fit 100 people at once, decorated with stained glass and marble statues. Next door, construction workers tear down an old hotel, leaving its once-grand rooms exposed to the weather outside.

Centuries of memories

Less than a kilometer away, Yuichi Miyabara sits in his concrete office building overlooking the lake. The Shinshu University professor arrived here in 2001 to study Lake Suwa and the disruptions to its natural rhythms. His team takes regular samples from the lake and analyzes them to closely track fluctuations in the water’s temperature and oxygen levels.

The only time his team avoids the lake is in the middle of winter. One of the first stories Miyabara heard when he arrived in Suwa was how a promising young researcher had died after falling through the ice decades earlier.

“This isn’t a place where you can play,” he says, explaining residents avoid swimming there even in summer because it was contaminated for decades by wastewater and later overrun by algae and weeds. “The lake is more of a place you look at from a distance.”

After a decades-long effort by the prefecture to divert wastewater and remove pesky weeds and algae, Suwa’s waters are noticeably cleaner now. But the natural circulation of the lake has also been disrupted by rising temperatures and shorter winters. Warm water is less dense and naturally sits above colder water, which sinks to the bottom of the lake. In the past, when summers were less hot and winters reliably cold, water at the lake’s surface and its depths would settle at similar temperatures, aiding circulation. This would ensure that oxygen mingled and saturated the entire lake.

Two decades ago, researchers at Suwa started noticing that dissolved oxygen levels 5 meters below the lake’s surface were frequently dropping well below 3 milligrams per liter in the summer, an environment uninhabitable for most fish, just as Fujimori had long predicted.

Recently, the prefectural government has tested a project that funnels “nano-bubbles” of compressed oxygen into the lake through a plastic hose. Similar tests in the past have been unsuccessful.

An official in the prefectural division in charge of the project said it is still awaiting results from the August study, but conceded that continuing the project would require a “considerable” budget and had to be weighed carefully.

The contraption is a neat idea, Miyabara says, but it’s hard to imagine how many machines it would take to pump enough oxygen into the lake.

“We’re not talking about a small body of water. It’s not like we can artificially mix the entire lake,” he says.

More than 20 years ago, John Magnuson, a longtime researcher of inland waters at the University of Wisconsin-Madison, was scouring the world for climate observations taken before the 1840s when he remembered Suwa. Magnuson flew to meet Miyasaka, the Shinto priest, and worked with a local researcher to trawl through the historic lake-ice data.

Magnuson found that since the advent of industrialization, ice began to freeze later in winter at Lake Suwa. In a 2016 paper published in Nature, Magnuson and his colleagues wrote that extreme warm weather had become more common in Suwa and attributed such changes to the increase in atmospheric carbon dioxide that has led to a rapid rise in local temperatures.

Annual air temperatures in Suwa have warmed at a rate of 2.4 degrees over the past century, double the national figure, according to the Meteorological Agency.

Between 1950 and 2014, Lake Suwa failed to freeze 17 times. In comparison, between 1443 to 1700, there were only three instances in which the lake didn’t freeze over completely. And when it comes to the omiwatari, the absences have grown more common: In the 1990s, it once disappeared for six consecutive years.

“There is something different about a human being looking at the lake, saying it iced over or broke up, that resonates more than complicated paleoclimate research,” says Magnuson, mentioning data taken from ice cores and tree rings that scientists can use to understand climate conditions from millions of years ago.

Human-made data have obvious shortfalls, Magnuson says, with sometimes damaged or partial recordings making it hard for researchers to draw large conclusions. “But it’s something people can relate to more easily, it’s something that makes more sense to them,” he says.

Scientists have since discovered even older data, like those taken since the ninth century at Bodensee, a lake that straddles the Swiss, German and Austrian border. Churches on opposite banks of the lake used to carry a bust of St. John the Evangelist across the ice every winter.

But Bodensee, also known as Lake Constance, stopped freezing in 1963, interrupting a centuries-old tradition. The religious relic is now permanently stored on the Swiss side of the water.

Magnuson predicts a similar fate for the Suwa omiwatari ritual. “The future generation may not see ice on Suwa,” he says.

Pausing on the phone, Magnuson asks after Miyasaka, and wonders if he has responded to a question about how he feels about the disappearance of the ice.

“I am curious how he feels about it, about the fact that he may be among the last to see the crossing,” he says.

Record booklets containing observations of ice cover on Lake Suwa and major events in the towns surrounding the lake from 1443 to 1681 are displayed at the Suwa City Museum in Nagano Prefecture. | REUTERS

Both ancient and fleeting

Miyasaka’s shrine is a picture of restraint and modest repose, its buildings made of bare wood stripped and roughened by the elements. Water drizzles out of a shallow pool carved from stone, and droplets glisten on the blue-green moss that covers it. Much like the central tenet that guides Shinto beliefs, the shrine, though centuries old, feels as if it is one with the greenery surrounding it, both ancient and fleeting at once.

The hushed reverence of the shrine is rudely disturbed by Miyasaka’s phone. His clamshell mobile rings incessantly with people asking him to approve festival plans and confirm venue reservations.

“Just give me the conclusion first, never mind the explanation,” Miyasaka says as he balances his phone on one shoulder. “OK, OK, OK, bye now,” he finally says, hanging up with a sigh.

Aside from the annual occurrences of the omiwatari, the shrine’s records also note major events in the towns surrounding the lake. In a particularly dramatic excerpt from the 1780s, Suwa’s records show how a nearby volcano erupted and caused a historic famine across Japan.

“From July the second, a great fire on Mount Asama raining ash,” he reads, tracing the page with his finger. “Roads blocked. … large fog cast … harvest ruined … villagers starving.”

His voice gets higher and louder with excitement as he flips the page. “What you learn is that people never write about good things; they only write about their difficulties,” he says. “When I read about these people tearing up the mountain to find something to eat, I realize again that people have always fought to survive, that hardship is the origin of everything.”

But with his knowledge of the sweep of history at the lake, how does he feel about the receding of the ice?

Every winter when a crowd of journalists asks him to give his verdict on yet another year without the omiwatari, he’ll throw out a pithy line to get laughs. Asked the same question now, he begins to tidy a pile of papers.

Miyasaka’s two sons left Suwa after high school, and both work in Tokyo. His oldest frequently travels abroad to conduct research for a large company.

“He’s tried to explain to me what exactly he does for work, but I can’t quite understand it,” he says as the sun lights up the room in amber. His daughter lives nearby and helps when she can around the shrine. It remains unclear who will be next in line to observe the lake after Miyasaka retires. It also remains to be seen if the omiwatari will disappear entirely as ice continues to thin over the lake.

“But we are here to keep watch,” Miyasaka says, “whether the ice disappears or not.”

Twilight on the lake

A few minutes after 4 p.m., as the sun begins to set, people begin gathering at the park overlooking the lake. Its waters still, the lake gradually turns tangerine, reflecting the clouds gathering above.

A young couple set up a small tripod for their iPhone and giggle as they dash into position, facing each other with their hands touching, the lake as their backdrop. They check through their burst of selfies, swiping the screen to find the perfect shot.

Nearby, an elderly woman in a crochet hat sits alone on a bench. She rubs her gloved hands together and takes in the scene. Fumiko Motokura, 84, comes to the park almost every day at this hour. She likes it here, a place with young people and foreign tourists, all mingling and waiting for the day to end.

“When I was a little girl, I could see the train come in every morning and see a line of workers walking along the lake to the watch factory there,” she says, pointing down toward the center of the town. “There was a training center here up on the hill where foreign students would come and learn how to make watches,” she said. The building is now abandoned.

She misses the omiwatari as a symbol of winter and a sign of a new, prosperous year. Recounting the myth of the god crossing the frozen lake to visit his love, she smiles with her whole face.

“It’s a romantic story, isn’t it?” she says.

The sun dips farther below the clouds and more visitors arrive, a few more of them acting out a memorable scene from an animated film released three years ago.

In the movie, a young woman and a man swap lives and bodies in their dreams, only to realize later that they are actually from separate timelines. The only place and time where they can reunite, a place free of all temporal restrictions, is at twilight above a lake that was inspired by Suwa.

As the sky deepens into night, a young woman steps out of her car and walks over to the edge of the park. She crosses her arms to keep warm and stares at the lake, her breath turning into vapor. In time, all that is left of the light disappears, and the lake fades into darkness at the center of town.