After first setting eyes on the Aztec capital of Tenochtitlán, Spanish conquistadores marveled in letters home about the beauty and engineering of the vast metropolis of over 200,000, rising from an artificially extended island in a region of mountain-valley lakes. But the Spanish went on to build a new city atop the original, one designed to dominate—rather than coexist with—the valley’s watery ecosystem. The result is that five centuries later, the successor capital known as Mexico City sprawls over drained lakebeds whose frequent flooding is dealt with by pumping water out of the valley. At the same time, the squandering of surface water and overuse of underground aquifers contribute to chronic water shortages, which, in turn, are addressed by pumping water back into the valley.

Scientists are warning that this precarious state of affairs will now be worsened by a US$13 billion airport being built atop the marshy, saline bed of what was once Lake Texcoco. They say the 4,430-hectare (10,947-acre) complex on the metropolis’s eastern fringe will increase flooding by hardening a large amount of lakebed land that currently accommodates excess water in the rainy season. And they warn that the ability of aquifers to recharge will suffer as well, since green areas around the lakebed that currently allow rainwater to seep underground will likely give way to impervious development spurred by the airport.

Critics of the project also cite the area’s role as a refuge for large numbers of migratory birds, which they say cannot coexist with the mammoth air-travel hub and extensive associated development planned for the area. The airport is projected to operate three runways and serve up to 50 million passengers a year starting in October 2020, with the capability of expanding to six runways and a 120-million-passenger annual capacity by 2065.

The focal point for this mega-development is land that Mexico’s National Commission for the Knowledge and Use of Biodiversity (Conabio) describes as an “area of importance for bird conservation.” The agency notes the presence there of over 100,000 birds among “1,700 hectares of permanent water and 2,000 hectares of seasonal pools that favor the establishment of large nesting and resting colonies of aquatic birds.” Conabio identifies “change in land use and development” as the two leading threats to the habitat.

More broadly, scientists lament that the project will effectively eliminate the largest vestige of the Aztec lake system, burying forever the dream that the modern metropolis might one day replicate Tenochitlán’s more harmonious relationship with the natural environment. Some experts have long advocated restoration of Lake Texcoco, the lowest point in the valley that is occupied by Mexico City, as a means of improving flood control in the basin, spurring growth in plant and animal populations and providing thermal regulation.

“This project is a disaster,” says Fernando Córdova, a leader of the Union of Scientists Committed to Society (UCCS), a nonprofit grouping of Mexican scientists focused largely on environmental issues. “The city is on the verge of a serious environmental crisis which means what we should be doing is looking for ways to slow this down. Lake Texcoco was a big part of the solution, and what the new airport does instead is accelerate the crisis.”

Few paid much attention when UCCS under Córdova’s leadership began voicing such concerns immediately after President Enrique Peña Nieto, with great fanfare, announced the new airport project in Sept. 2014. Meanwhile, local residents complain that authorities and the media largely ignored their objections to the start of construction in 2015 and to the dynamiting and excavation of rock used to build up the lakebed site. “Thanks to its size, design and social benefits, the new airport will be a transcendental construction that will be emblematic of modern Mexico,” President Peña pledged when he unveiled his legacy project.

The airport plan calls for a 74-hectare (183-acre) terminal whose design by British architect Norman Foster resembles a four-legged spider. Extensive hotel, shopping, convention and industrial development planned nearby has been dubbed the Aerotrópolis—a virtual city that project promoters claim will employ 180,000 people. Pushed by the government, business groups and private-sector luminaries such as telecom tycoon Carlos Slim, one of the world’s richest men, the project has gathered seemingly unstoppable momentum, especially since construction began three years ago.

But the airport’s aura of inevitability developed some fissures at the outset of this year’s campaign for the Mexican presidency. That’s when left-leaning frontrunner—and eventual victor—Andrés Manuel López Obrador promised he would scupper the project, denouncing it as a hotbed of corruption and a colossal waste of money. While acknowledging the city’s existing airport is overstretched, he argued that it would be more practical and far cheaper to augment air-traffic capacity by building two new runways at the military base of Santa Lucia. The new airport is being built a few miles east of the current one, Benito Juárez, which will have to be closed when the new airfield opens. López Obrador says experts have assured him that the Santa Lucia base, which lies 25 miles to the northeast, could offer expanded service without impinging on Benito Juárez’s operations.

When a chorus of powerful business leaders angrily accused López Obrador of spooking investors with his airport stance, the candidate hinted he might favor continuing the project if it were entirely funded by the private sector. But since winning the July 1 election in a landslide, López Obrador has further adjusted his position. He has ordered his transition team to review two options—continuing the project as currently planned or expanding Santa Lucia—and to use the exercise as a springboard for a national discussion culminating in some form of public consultation.

The team, headed by Javier Jiménez Espriú, an engineer López Obrador has tapped as the next transport minister, briefly outlined the pros and cons of each alternative in an Aug. 17 press conference. Addressing the current airport plan, Jiménez Espriú cited effects on bird habitat and “other negative environmental impacts.” He acknowledged there are questions about whether Benito Juárez and an expanded Santa Lucia airport could operate simultaneously, but said these would be studied. Meanwhile, López Obrador recently announced the consultation will occur at the end of October. Though he doesn’t take office until Dec. 1, he said his government will be guided by the result of the exercise, offering no further details.

López Obrador has never made much of environmental concerns in his airport statements, but there are signs that some on his team take such issues seriously. Córdova, the UCCS member, says that during the campaign he met with Jiménez Espriú, who has invited Córdova to participate in the airport-project review. Says Córdova: “I had the impression he understands how grave the situation is and what a mistake it is to carry through with the project, but that he also understands how complicated it would be to stop it.”

Josefa González Blanco, López Obrador’s choice to head the Environment and Natural Resources Secretariat (Semarnat), underscored recently that when it comes to the airport project, environmental concerns might be gaining some traction. “We have to study what the impacts will really be,” she told reporters earlier this month. “Many of the existing studies are not truthful, such as the environmental-impact study, which is missing many elements.”

The impact study was submitted in September 2014 by the state-owned company set up to oversee the project—Mexico City Airport Group (GACM). Semarnat, Mexico’s lead environmental agency, green-lighted the study in November with only minor conditions. But the study is both superficial and woefully incomplete, according to an analysis of it that Córdova coordinated for the UCCS. The analysis cites various shortfalls, among them a lack of technical information on flood-control infrastructure. The UCCS also faults the study for underestimating the population and variety of birds; assuming the birds will readily nest elsewhere; and pledging to “duplicate and improve” surface-water supplies for remaining bird habitat without explaining how it will do so.

According to the Western Hemisphere Shorebird Reserve Network, the area serves as particularly important migratory habitat for the Wilson’s phalarope (Phalaropus tricolor) and also hosts “significant numbers” of Baird’s sandpiper (Calidris bairdii), least sandpiper (Calidris minutilla) and western sandpiper (Calidris mauri). Migratory birds currently concentrate around Nabor Carrillo Lake, an artificially bolstered portion of the Texcoco lakebed that was made into a permanent body of water in 1982 to spur long-term efforts toward partial restoration of the region’s wetland ecosystem.

The environmental-impact study describes improvements planned for Nabor Carrillo, but the National Water Commission announced in May that the strategy has changed and that the lake will now be partially drained and converted into a catchment basin for use in connection with rainy-season flood control.

“The birds go there precisely because the conditions are propitious for them to take refuge and to build their nests,” says Omar Arellano, an expert in ecotoxicology who took part in the UCCS analysis of the environmental-impact study. “This is an issue of ecological functionality.”

Also ignored in the study, critics say, was extensive excavation of rock in the hills on the valley’s eastern side as fill for the airport site. Local complaints have focused not only on this digging, but also on the proliferation of dump sites for mud removed from the lakebed. José Espino, an agronomist at Autonomous Chapingo University in Texcoco, the country’s flagship university for agricultural science, lives close to some of the dumps in the community of San Nicolás Tlaminca. He says he worries about salts from sludge leeching into the aquifer and contaminating water used for irrigation and drinking. Espino says members of his activist group, United Neighbors of Tlaminca, are struggling to get their concerns heard.

“We got the big site closed last October, but that has only made the problem worse,” he says. “They still keep bringing waste, but now they dump it in numerous small sites instead.”

Espino says the government refuses to explain what is happening. He charges that this lack of transparency, coupled with the fragmentation of the permitting and impact-study process into multiple exercises, complicates the ability of his and other communities to understand and respond to the project. Opponents of the airport charge such tactics are being used to pave the way for associated infrastructure projects including access roads, rail links as well as the various components of the Aerotrópolis. These ingredients, the critics allege, were deliberately ignored in the main environmental impact study so assessment of them could be divided up in a confusing welter of individual studies that mask the airport’s overall environmental effects. “The airport will have a major impact on the whole region that the environmental-impact study doesn’t take into account,” says Arellano, the ecotoxicologist. “This is not just about runways and terminal buildings, but a series of other projects that will detonate other changes too.”

In the GACM offices, Alejandro Virchez, the official in charge of ensuring the new airport meets its environmental obligations, leans back in his chair and sighs when asked to respond to such criticism. “Everything is considered damaging,” he says. “No, development is not in a fight with environment. Every project has collateral effects and the issue is to mitigate them according to the law, which is what we are doing.” Virchez insists that concern about migratory birds is exaggerated because there is a plan to improve bodies of water elsewhere in the metropolis to serve as new refuges. He also says rock extraction in the valley’s eastern hills predates the airport project and that his job is simply to ensure that the companies doing the work have their permits in order.

Blow to wetland restoration?

Asked about the wider issue of whether the project destroys chances of recuperating parts of the valley’s natural lake system, he responds that Lake Texcoco has been dry for a century. That assertion is challenged by scientists opposing the project who point to wetland restoration efforts begun in the 1970s. The projects, the scientists say, have boosted habitat and bird populations—progress, they add, that will be reversed by the airport project.

Virchez acknowledges GACM could have been “better at responding” more quickly to environmental concerns, thereby boosting public confidence that major impacts would be mitigated properly. But he insists that any environmental drawbacks are far outweighed by regional and national development gains. “The infrastructure is necessary, so what do you want, to detain the growth of the country?” he asks. “This is a macro issue.”

Scientists such as Córdova and Arellano expect business pressure will prompt López Obrador to forge ahead with the project, but they are buoyed by the promise of a review. Says Arellano: “When I think with my heart, I think this could be stopped and that this would set a precedent for projects like these.”

Thus far, however, there has been little indication nongovernmental groups will weigh in on the issue in a substantial way, even though López Obrador’s appears to have created space for renewed debate. A spokesman for the World Wildlife Fund (WWF), Gerardo Tena, notes his group rarely works on issues within the city. He says he does not know whether WWF has plans to take part in the consultation process, adding: “But it’s a good question.”

Monitoring initiative fizzles

The Mexican Center for Environmental Law (Cemda) entered the fray after the project was unveiled in 2014, joining a civil-society “Citizen’s Observatory” initiative to monitor the project for transparency, socioeconomic benefits and environmental sustainability. The Observatory issued a report in 2015 highlighting concerns about planning transparency, bird-habitat impact and other matters, but the initiative then faded away. Cemda spokesperson Margarita Campuzano says the group had become overstretched by other priorities.

For their part, local activists hope López Obrador’s election will create fertile ground for broad-based organizing of those concerned about the project. “On July 1st the atmosphere in this country completely changed,” says América del Valle, an activist from the town of San Salvador Atenco, which lies next to the new airport. Del Valle helped lead a movement that successfully forced President Vicente Fox to scrap plans for a smaller airport in the same area.

The Atenco movement went on to organize confrontational protests against a whole range of projects it deemed to be “against the people.” It was dismantled in 2006, after a violent demonstration against a government crackdown on street vendors was met with an even more violent police response. That response was ordered by the governor of the state of Mexico at the time—Enrique Peña Nieto, who is slated to hand Mexico’s presidency over to his successor, López Obrador, on Dec. 1. Several Atenco leaders spent years in high-security prison. After being released, they find themselves once again protesting—this time against an even bigger airport project promoted by their nemesis.