In the early 2000s, a 1,750-hectare (4,300-acre) swath of low-lying land in the Paraná River flood zone just outside Buenos Aires began to be transformed into a sprawling residential development dotted with green spaces and artificial ponds. Called Nordelta, the development was built on millions of tons of soil dug at the site and piled up to create housing pads and embankments high enough to prevent flooding.

Today, about 45,000 people live in Nordelta, located in the municipality of Tigre, 25 kilometers (16 miles) north of the Argentine capital. There are 5,000 houses, some valued at up to US$6 million, but there are also 7,000 apartments, some with only one or two bedrooms.

There are other residents, too, original ones whose population according to homeowners has increased dramatically over the past decade, causing consternation among the humans who now call Nordelta home. These residents are capybaras (Hydrochoerus hydrochaeris), the world’s largest rodent. Native to South America, capybaras can weigh over 150 pounds. Their numbers in Nordelta are estimated at 1,000.

Large groups of the rodents troop into gardens and houses and roadways, causing property damage, frightening children, and disrupting traffic. The result has been disagreement between residents, who have begun taking steps to reduce the capybara population, and environmental advocates, who are pressing for the rodent’s protection.

While authorities struggle to find a solution that satisfies everyone, the dispute has reached the courts, highlighting a lack of adequate land-use controls to regulate the expansion of urbanization and industry into natural ecosystems. Attempts to address the problem in Congress have thus far failed. For instance, a coalition of scientists and environmentalists have called for over a decade for the enactment of wetland-protection legislation, citing the importance of wetlands in supporting biodiversity, mitigating floods, and serving as carbon sinks. But bills drafted to regulate development near wetlands have failed to muster sufficient support amid opposition from the real estate-development and farming lobbies.

The result has been a regulatory vacuum.

“Nordelta didn’t just slightly alter the wetland; it completely transformed it to create artificial lagoons and parks,” says biologist and ecologist Roberto Bo. “This problem could have been avoided if natural patches had been left undeveloped and unmodified, connected by land and water corridors, but they didn’t do that, evidently to maximize their real estate profits.”

Adds Bo: “Today, I understand the frustration of Nordelta residents, who a few years ago had no idea this would happen. But drastic solutions, like relocating the capybaras or promoting hunting, wouldn’t work: the animals would return within a few years.”

Unregulated construction

Bo says there’s a broader concern about the continued, unplanned expansion of residential development throughout the flood zone near the mouth of the Paraná River.

Says Marcelo Cantón, communications manager of the Nordelta Neighborhood Association: “I’ve lived in Nordelta for 25 years, and until ten years ago I had never seen a capybara. Today, they’re everywhere. Last year, a family of 17 lived in the lagoon across from my house, and now there are more than 30. There’s an estimated population of 1,000 animals, and the biologists who work with us have detected population growth of up to 100% in a single year. Our goal is to achieve a harmonious coexistence with the capybaras. To do this, we need to find the best way to moderate population growth.”

With the approval of the Buenos Aires provincial government, residents of Nordelta last year launched a sterilization and chemical vasectomy program, the results of which are still being evaluated. The program was challenged in court by an animal rights organization, which requested that wildlife in the Tigre wetlands be recognized as having rights. The group also asked that environmental-impact studies of Nordelta’s effects be conducted.

Earlier this month, a judge granted a temporary injunction suspending the sterilization of capybaras, but the decision was overturned by another judge a few days later.

“The habitat of the capybaras, who were there before Nordelta was built, has been transformed,” says María de las Victorias González Silvano, the plaintiff’s attorney in the case and a professor of Animal Law at the University of Buenos Aires (UBA). “We seek to protect ecosystems so animals and people can coexist. We’re fighting against a very powerful enemy because wealthy people live in Nordelta. But we understand this case can set an important precedent in Argentina, limiting real estate development that wants to encroach on animal habitat.”

Sheltered existence

Not all specialists agree. Biologist Aníbal Parera, author of the book “Mammals of Argentina and Southern South America,” sees the capybaras as thriving in Nordelta’s artificial environment rather than being oppressed by it.

“This is an amphibious rodent that in Nordelta easily finds both food—all kinds of vegetation, both natural and cultivated—and the water it needs in a safe environment, because there are no people hunting them for food or stray dogs chasing them as in other environments,” Parera tells EcoAméricas. “For this reason, and because of their high reproductive capacity, there is now an overpopulation.”

Parera supports immediate intervention to reduce capybara populations humanely: “If nothing is done, they will continue to multiply until they run out of food, creating a dangerous situation where they attack each other or become ill. We could consider relocating capybaras to natural areas where they are scarce or proceeding with sterilization programs.”

Other experts, while agreeing Nordelta’s conditions are favorable for capybaras, emphasize that the broader problem is the toll unplanned growth takes on wetlands. “The serious problem is the ongoing disappearance of wetlands, which is transforming ecosystems due to the expansion of urban developments without environmental-impact studies or land-use planning,” says biologist Rubén Quintana, president of the Argentine branch of the global conservation group Wetlands International.