ROSARIO, Argentina — The fisherman woke up early on a recent morning, banged on the fuel containers on his small boat to make sure he had enough for the day, and set out on the Paraná River, fishing net in hand.
The outing was a waste of time. The river, an economic lifeline in South America, has shrunk significantly amid a severe drought, and the effects are damaging lives and livelihoods along its banks and well beyond.
“I didn’t catch a single fish,” said the 68-year-old fisherman, Juan Carlos Garate, pointing to patches of grass sprouting where there used to be water. “Everything is dry.”
The Paraná’s reduced flow, at its lowest level since the 1940s, has upended delicate ecosystems in the vast area that straddles Brazil, Argentina and Paraguay and left scores of communities scrambling for fresh water.
In a region that depends heavily on rivers to generate power and to transport the agricultural commodities that are a pillar of national economies, the retreat of the continent’s second-largest river has also hurt business, increasing the costs of energy production and shipping.
Experts say deforestation in the Amazon, along with rain patterns altered by a warming planet, are helping fuel the drought. Much of the humidity that turns into the rain that feeds tributaries of the Paraná originates in the Amazon rainforest, where trees release water vapor in a process scientists call “flying rivers.”
Rampant deforestation has disrupted this flow of humidity, weakening the streams that feed the larger rivers in the basin — and transforming the landscape.
“This is much more than a water problem,” said Lucas Micheloud, a Rosario-based member of the Argentine Association of Environmental Lawyers. Frequent fires, he said, are turning resource-rich rain forests into savannas.
Although water level varies in different locations, on average the Paraná is now 10.5 feet below its normal flow, according to Juan Borus, an expert at Argentina’s government-run National Water Institute who has been studying the river for more than three decades.
The situation is likely to worsen at least through the beginning of November, which marks the beginning of the rainy season in the region, but the drought could last longer. Experts say climate change has made it harder to make accurate predictions.
Extreme events like the drought affecting much of South America are becoming “more frequent and more intense,” said Lincoln Alves, a researcher at Brazil’s National Institute of Space Research who worked on the latest report by the United Nations Intergovernmental Panel on Climate Change.
Argentina declared a six-month emergency for the Paraná River region in late July, calling the crisis the worst in 77 years. Government officials say they were caught off guard.
“We never thought we were going to reach the levels we are now,” said Gabriel Fuks, who leads a team that coordinates the government’s response to emergencies across the country. “We were not prepared for this emergency.”
The biggest priority for the government is assisting the approximately 60 cities along the river that are running dangerously low on water, Mr. Fuks said.
In Paraná, a riverside city some 125 miles from Rosario, a pump that supplies 15 percent of the water to the city of 250,000 stopped working recently because the water level was too low. City officials had to hastily devise a solution, said Leonardo Marsilli, the city’s technical coordinator of water services.
All along the river, the low water levels are affecting daily life.
For Luciano Fabián Carrizo, a 15-year-old who lives in El Espinillo, the same river island community as Mr. Garate, the fisherman, the sudden disappearance of water means he now has to walk two hours to get to school. The commute used to take him 15 minutes by boat.
Across the river, at Terminal Puerto Rosario, one of the city’s ports, officials had to extend the arms of cranes by more than six feet in order to reach ships, said Gustavo Nardelli, one of the port’s directors.
And in downtown Rosario, Guillermo Wade, the head of the Maritime and Port Activities Chamber, does feverish calculations each morning to figure out how much can be loaded onto cargo ships without the risk of getting stuck along the river’s shallowest portions.
Ships have been loading 26 percent less cargo than normal. Mr. Wade fears that number could reach as high as 65 percent later this year if the most dire predictions materialize.
“We are losing an outrageous amount of cargo,” Mr. Wade said.
Shipowners are also increasing costs to compensate for the risk of getting stuck in the shallows.
The average price of a shipping voyage has more than doubled since May, from $15,000 per day to $35,000, according to Gustavo Idígoras, the head of the Ciara-Cec chamber that represents grain exporting companies.
The shallow Paraná River raised the cost of exporting agricultural products from Argentina by $315 million over all between March and August, according to an estimate by the Rosario Board of Trade. More than 80 percent of the country’s agricultural exports, including almost all of its soybeans, the country’s top cash crop, take the river to the Atlantic Ocean.
The lack of water is also making energy more expensive for both Argentina and Brazil, where underperforming dams are forcing governments to rely more heavily on costlier sources of energy.
The Club Náutico Sportivo Avellaneda, a nautical club on the river’s edge in Rosario, had to reinforce docks that were suddenly at risk of collapse. Sail boats and small yachts are grounded.
“This section generally has four meters of water, and now it’s completely dry,” said Pablo Creolani, the club president. “We never thought something like this could happen.”
Scientists say this type of drought is likely to become more common in the future and bring about changes in the local ecosystem that could prove irreversible.
“Maybe this isn’t the new normal, but it’s a new situation that won’t be that infrequent anymore,” said Walter Collischonn, a hydrologist at Brazil’s Federal University of Rio Grande do Sul.
Some blame Brazil, Argentina’s giant neighbor, where environmental protection agencies have been hollowed out and the government is seeking to make it easier to mine and develop land in the Amazon.
“This is all thanks to the disaster that they’re carrying out in Brazil. They chopped down everything,” said Gabriel Callegri, a 50-year-old fisherman from El Espinillo. “Who isn’t angry about that?”
Viviana Aguilar, a 60-year-old retiree who has been rowing along the Paraná River for more than two decades, finds it hard to believe how much the landscape has changed in the past year as islands have emerged where there was once only water.
“It’s humanity that is putting nature at risk,” she said.
Manuela Andreoni contributed reporting from Rio de Janeiro.