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The main artery that cuts through Italy's heartland, where 30% of its food is produced, is the 650-kilometre-long (400-mile-long) River Po, which winds its way from the Alps to the Adriatic Sea on Italy's northeast coast. But a dry winter and spring mean this year it's in trouble.

The "Big River," as it is known, plays an integral role in the nation's history. Before bridges were built, its deep waters protected civilizations on either side from invaders who could not cross.

In later years, cities and industries sprouted on its banks and made use of the water for hydropower, transportation and irrigation. Along some sections of the River Po, processing plants turn the muddy river into drinking water.

The Po is fed by winter snow in the Alps and heavy rainfall in the spring that often leads to devastating floods. At a café near the banks of the river, close to the city of Mantova, a measuring stick on the wall indicates how high the water has risen. In 1951, it nearly touched the roof.

But in 2022, things are very different. An unusually dry winter meant snow melt was scarce and spring rains only sporadic, which has led to the worst drought in the northern regions of Italy in more than 70 years, a regional agency for the River Po confirmed.

As a result, the Po is hitting record low water levels, according to the European Space Agency. An animation from the agency's Copernicus Sentinel-2 satellite mission reveals how the river has "significantly shrunk" between June 2020 and June 2022.

And that is a big problem for the millions of people who rely on the Po for their livelihoods. Salination from the Adriatic Sea has started turning its fresh water into unusable poison for crops. Recent samples show salt water more than 20 kilometres (12 miles) inland, and as the river drops lower, the sea will continue to fill the void.

Massimiliano Fazzini, head of the Climate Risk Department of the Italian Society of Environmental Geology, says that in the current hydrological year, which started December 1, the Po River basin has a water deficit of around 45% to 70% in some areas.

"I'm usually never a pessimistic or alarmist, but this time we must be alarmist," he told CNN, citing the difference in the average snowfall from 7.5 metres (24.6 feet) in normal years to 2.5 metres (8.2 feet) this year coupled with rising temperatures that have meant the reservoirs that might be accessible in a drought year are not at capacity. "The situation is critical and can only get worse," he said.

At Simone Minelli's dairy farm along the banks of the river near Mantova, the prospect is grim. Water is an essential part of the operation to feed his herd of 300 Friesian cattle, he told CNN.

His milk cows produce 30 litres (6.6 gallons) of milk each a day that is transformed into this region's authentic Parmigiano Reggiano parmesan cheese. If his cows don't each drink between 100 and 150 litres (22 to 33 gallons) of water a day or are overheated, the milk won't meet the rigid standards, and the cheese won't be given the coveted seal of approval.

But a bigger concern than the water in their troughs is what they'll eat. Minelli primarily uses water from the Po for irrigation of crops to feed his cattle. He showed CNN a soybean field that has not been irrigated and is suffering with small, withered plants that won't nourish his cattle.

He is worried about restrictions on water as he watches the Po level go down even further -- and where he could even buy feed if other farmers are suffering similarly. "I'm very worried, we take it day by day," he said. "If you don't have enough food to feed your cattle, you have to reduce," he said, referring to the number of cows in his herd.

In the nearby Parmigiano Reggiano consortium, his milk is mixed with that of 20 other dairy farmers to produce 52,000 rounds of the coveted cheese each year. If the milk runs dry, the cheese won't get made.

Further up the river, Ada Giorgi showed CNN the pump house operated by the consortium she has presided over for 20 years. The consortium has had to pay to have sand removed from the riverbed so the pumps don't get clogged, she said, and has added one meter (3.3 feet) of pipe to lower the pumps even more if the water level continues to drop. The water from the pump house feeds a labyrinth of canals leading to irrigation hubs and processing plants.

The consortium's 150,000 customers are still receiving water, but as Giorgi looks at the level of the Po, she says she is worried about the future. "The last time the river was low was 2003," she told CNN. "This time it is much, much worse. There is a lack of rain, no snow, and high temperatures," she said. "It creates the famous perfect storm. We are in extreme crisis."

If it doesn't rain -- and no meaningful rain is forecast in the near future -- things will only get worse. In the city of Milan, Italy's financial hub, the mayor has all ornamental fountains turned off, and prohibited the washing of private vehicles or watering of gardens and lawns.

In the small town of Castenaso, close to Bologna, hairdressers and barbers are reportedly prohibited from washing clients' hair twice in an attempt to save water before supplies there run too low.

Meanwhile, a grueling heatwave has gripped much of southern Italy since May.

Scientists call the Mediterranean region a . The human-caused crisis has made and intense, and has led to less rainfall in the summer. Temperatures are expected to be between 20% and 50% hotter than the global average, and droughts here will worsen by mid-century, even if the world does dial down its greenhouse gas emissions. If emissions continue at very high levels, droughts and wildfires will become so severe that continuing agriculture will be difficult. Tourism will also become less attractive.

Italy is a net exporter of food, providing goods like wheat to many developing nations. A drought here is only exacerbating a food crisis being felt acutely in poorer parts of the world. And the River Po holds an outsize significance for Italians.

Author Tobias Jones, whose book "The Po -- An Elegy for Italy's Longest River" traces the river's history, followed the entire length of the river to capture its importance. He says the Po is to Italy what the Thames is to London or the Mississippi is to the United States.

"For centuries, the worry was about the river flooding, but climate change has meant that the river is now at risk of drying up," he told CNN.

"It is not just a river, it is part of the national psyche. The towns along it draw tourism and industry. It was almost a moat for central Italy that kept it safe from invaders. Now it is under threat and no one knows what to do to save it."