Their proliferation is fueling an ardent debate in Argentina on environmental protection and inequalities in the country where 42% of the population is considered poor.
True "closed" city with its individual houses all equipped with a swimming pool, its sports complexes, its places of worship and its schools, Nordelta boasts of offering "the tranquility of nature and the comfort of the city" to its rich inhabitants in search of security and social homogeneity, with its segmented neighborhoods and private security guards.
Built 20 years ago, Nordelta was erected on the marshy areas at the mouth of the Parana River which flows into the Rio de la Plata north of Buenos Aires.
The complex now covers 1.600 hectares where once peacefully waded families of cabiais, these water pigs also called capybara (Hydrochoerus hydrochaeris), the largest rodent in the world that can weigh up to 80 kilos.
"Live with them"
"The capybaras have always been there. We saw a few of them from time to time. But three or four months ago, they (the real estate developers) attacked their last refuge causing the stampede", explains to the AFP Perla Paggi, a neighbor of Nordelta who pleads for the preservation of these herbivorous mammals.
The clearing of the only virgin land remaining to build a private clinic has dislodged hundreds of families who have invaded the upscale neighborhoods.
"We must learn to live with them, they are not aggressive animals. They are defenseless, we lock them up, we deprive them of their habitat and now we complain because they invade us", blows Ms. Paggi who pleads for the establishment of a "reserve of 20 or 30 hectares to maintain diversity".
"Nordelta was a very rich wetland which should never have been touched. But now that the damage is done, the neighbors must reach a certain level of coexistence with the capybaras", adds the biologist Sebastian di Martino, director of the conservation at the Rewilding Argentina Foundation.
"But it's not that simple," he warns, believing that the creation of a reserve will not be enough to contain the expanding population, a female can make a litter of six young each year.
"We must keep them away from children and pets. And we will have to find a way to regulate their population, perhaps by moving them to other places," said Mr. Di Martino.
Selfies and memes
While waiting for a solution, the cabiais have become a photographic attraction in Nordelta and a topic of conversation in Argentina.
Social networks are full of selfies and memes, some hailing a new "class war" with the cabiais who have come to reclaim their lands usurped by the rich inhabitants of Nordelta.
A photomontage of a Cabiais reading "Capital" by Karl Marx was widely shared around the hashtag "#carpinchosvsChetos" (the cabiais against the bourgeois, editor's note).
The inhabitants of Nordelta publish videos of traffic accidents caused by cabiais dangerously crossing the roads, photos of overturned trash cans or even of a dog apparently bitten by the semi-aquatic animal.
The proliferation of cabiais is not a problem specific to Nordelta but also for "many regions of the country, urbanized or not", notes the biologist.
Sebastian di Martino points to "the alteration and degradation of ecosystems" which have "wiped out many species that were their natural predators".
Cabiais is a delicacy of choice for jaguars, pumas, foxes, dogs and wild cats, but their populations are almost extinct in Argentina.
"Without a predator which regulates its population and also generates fear", the cabiai "no longer hides and spends all day eating", he notes.
A trend reversal for this species which 20 years ago was threatened by intensive hunting.
"Their skins were very popular for fur ... but this fashion has passed," says Mr. Di Martino.