Mymba Kuéra: what the monumental rescue of more than 30,000 animals was like during the construction of Itaipu, between Brazil and Paraguay

"It was a great challenge. Paraguay had never done anything like it, we were the pioneers." Darío Pérez Chena was 43 years old when he led one of the largest wildlife rescues in Latin American history.

The Paraguayan agronomist engineer directed the team that, in 1982, saved thousands of animals in a race against time: from monkeys to armadillos, snakes and tarantulas.

Pérez Chena worked for Itaipu Binacional, the organization created by an agreement between Brazil and Paraguay, which was tasked with building a colossal engineering project on the Paraná River. With more than 7 km in length, the Itaipu power plant became, at the time, the largest hydroelectric dam in the world.

The engineer had graduated in Paraguay and returned to the country's capital, Asunción, after his postgraduate studies in Germany. He was director of Paraguay's National Forestry Service, until he decided to take on another great challenge.

Pérez Chena moved, with his wife and children, to the city of Puerto Stroessner, today Ciudad del Este, on the border with Brazil. He became responsible for terrestrial fauna and flora at Itaipu.

His work in the historic rescue of local wildlife defined the foundations for biodiversity protection in the region, which remain in place to this day.

Pérez Chena recounted how the titanic operation unfolded to journalist Stefania Gozzer, from the BBC World Service radio program Witness History.

A treasure of biodiversity

The construction of the Itaipu dam took nine years. Around 40,000 people worked on it. To carry out the work on dry ground, it was necessary to excavate a canal to temporarily divert the river.

The work was completed in 1982. Everything was ready to open the floodgates and begin filling the dam's gigantic reservoir, covering approximately 1,350 km², with water.

But the region to be flooded was part of a vast ecosystem: the Upper Paraná Atlantic Forest, one of the planet's richest areas of biodiversity. This habitat is home to around 20,000 plant species and at least 2,000 animal species, such as pumas and jaguars, as well as 400 bird species.

The construction of Itaipu coincided with a new era in the history of ecology, initiated by the United Nations Conference on the Human Environment, held in the Swedish capital in 1972. The Stockholm Conference made the environment a fundamental issue.

And the Itaipu wildlife rescue sparked enormous interest around the world. Could that biodiversity treasure be saved, at least in part?

Brazil and Paraguay took on the task of rescuing the wild fauna from their respective sides of the river. And on the Paraguayan side, the wildlife recovery project was given the name Mymba Kuéra — "the animals," in the Guaraní language.

189 people

Preparations for the rescue took several years. They included carrying out an inventory of the entire affected area, with the participation of botanists, zoologists and forestry engineers, among other professionals.

Each sighting was recorded and animals were also identified by their traces, such as footprints or fecal matter. "The terrain allowed for the construction of a large archive of Paraguayan fauna," engineer Pérez Chena told the BBC.

"We contributed greatly to the knowledge of that region. And we also offered the opportunity to learn to many biology, veterinary and agronomy students." The inventory was the basis of the rescue operation, which would be carried out by a team of 189 people, led by Pérez Chena.

"The team was very well selected," he recalls. "We tried to bring young people, no older than 40 or 45 years old, who could swim, who had good eyesight and good hearing."

The rescuers traveled by speedboat and communicated by radio, frequently in Guaraní. "The technology was different back then," recalls Pérez Chena. "We didn't have cordless phones, we had old radios and the boat engines were less advanced than today's."

"We used equipment that today is practically museum pieces, but with it we accomplished something that is still analyzed and remembered to this day."

In addition to the 189 people in charge of the rescue, there was a support team of another 150 people, including doctors, nurses, helicopter pilots, mechanics and firefighters. All of them stayed in the housing complexes built especially for the Itaipu construction works.

The rescuers were trained by Brazilian and other countries' technicians. "With this wealth of knowledge and human resources, we set out on the adventure on October 13, 1982," the agronomist recounts.

Race against time

On that October 13, the floodgates of the diversion channel were closed and the lake area began to flood. The animal rescue began as the water rose. Initially, few animals were recovered, but the number increased rapidly, reaching a peak of more than 600 in a single day.

"We only saved the animals that couldn't swim," says Pérez Chena. "Someone asked me: 'How many jaguars did you save?' I replied: 'None.' Because the jaguar is a great swimmer and doesn't need to be saved."

"There are even jaguars that cross the Paraná River, from Paraguay to Brazil and from Brazil to Paraguay," he explains.

Pérez Chena recalls that monkeys know how to swim, but they get tired and can drown. "In the water, many animals are completely defenseless," he says. "They concentrate all their energy on saving themselves. That's why it's easy to catch them with a net or a lasso."

"We rescued female monkeys with small babies hanging from their necks. It seemed as though they were crying at losing their freedom." The workers were trained to deal with aggressive animals, tarantulas and venomous snakes.

"There are vipers with venom so toxic that you have to act within minutes," according to Pérez Chena. "In each boat, we had a kit with antivenom serum for use in emergencies." The agronomist did not expect to need to rescue birds, but he saved many of them as well.

"We found birds floundering in the water," he recalls. "They would climb onto tree branches to hunt insects and sometimes got their tail feathers wet — the feathers that serve as their rudder. We had to start looking for special cages to collect birds."

The rescue operation continued until January 10, 1983. "In total, we saved 27,150 animals. Of these, 45% were snakes and half of them were venomous." On the Brazilian side, the forest was smaller and there were more cultivated areas. For this reason, only around 11,000 animals were rescued.

"Adding it all together, that's nearly 39,000 animals, a record for South America to this day," Pérez Chena emphasizes.

Snakes and armadillos

Many of the animals were transferred to more than 100,000 hectares of protected areas within the same Atlantic Forest ecosystem. Hundreds of vipers were sent to the Butantan Institute in São Paulo, a leader in biological research and in the production of antivenom serums and other pharmaceutical products.

"At six o'clock in the morning, the first plane would leave every day, carrying the crates of snakes to São Paulo," recalls Pérez Chena. Some six-banded armadillos ended up in Japan. "It is one of the few animals resistant to leprosy," explains the engineer. "Those armadillos from Alto Paraná ended up in Tokyo for scientific research."

Pérez Chena acknowledges that, despite the vast operation, many animals could not be rescued. "We saved many animals, but many others probably died," he laments.

"Insects, for example. We don't know how many animals that lived underground ended up becoming part of the soil's organic matter. We admit that mistakes were made, but never out of negligence," explains the agronomist. "Only out of inexperience."

"We always worked with clean hands, with a clear conscience that we were doing something positive for the world. We worked with great honesty, within the bounds of what we knew and believed we were doing well. We had great conviction."

He highlights that the operation brought the rescuers closer together. "We protected one another all day long. We had no serious accidents. Only minor monkey bites, but all 189 of us came back."

'It was a source of pride'

Today, the Itaipu hydroelectric plant supplies approximately 86% of Paraguay's electricity market and 9% of Brazil's. Paraguay sells part of its generated energy to Brazil and is therefore an electricity-exporting country.

The great hydroelectric project was only surpassed in size and generating capacity by the Three Gorges Dam in China, completed in 2012. But Itaipu maintains the world record for accumulated energy produced over its more than 40 years of operation.

Pérez Chena is now 87 years old. He lives in Asunción with his wife Lucina. Their marriage brought four children and 12 grandchildren. The agronomist is grateful to this day that the team of 189 men survived the rescue mission. Of them, "perhaps 50 or 60 are still alive," according to him.

The 1982 fauna rescue laid the groundwork for current reserves and biodiversity projects, such as the Itaipu Tekotopa Environmental Center in the Paraguayan city of Hernandarias, near the dam.

Over the years, Operation Mymba Kuéra received various forms of recognition. "We received international titles as great defenders of nature," says Pérez Chena. "But perhaps the most beautiful thing is that we did something positive for the biodiversity of that region."

Darío Pérez Chena believes it is important to keep sharing the story of that historic rescue. "Sometimes people say that what is past is past. But the past must teach us not to make the same mistakes," the Paraguayan engineer told the BBC.

"That is why I say that history is life's teacher. For us, it was a source of pride to have worked on saving the animals before they were lost. We left a footprint that is still followed to this day."