Mexico City’s small urban farms — known locally as chinampas — practice a sort of agriculture in reverse: instead of bringing water to land as most farms do, chinampas bring land to water.

The chinampas in use today go back about a thousand years, to when Aztec farmers began building rectangular fields on top of vast lakes and growing food for what was then the city of Tenochtitlan. There were tens of thousands of chinampas at one point, arranged in strict grids with narrow canals between them, though many were destroyed or abandoned (along with the rest of the Mesoamerican metropolis) after Hernán Cortés and his invading Spanish soldiers rearranged the civic order in 1521.

But working chinampas continue to exist in the southern Mexico City neighborhood of Xochimilco — despite continuing encroachment by developers and competition from factory farms — operating mostly as family businesses that produce heirloom lettuce, radishes, dahlias and other crops. Lately, the farms’ irrigation-friendly ways are getting fresh attention in a world rocked by climate change and suffering from widespread droughts.

Could other places around the globe borrow the idea of creating “floating islands,” as the fields are sometimes called, which are engulfed by water? A team of Mexican designers, landscapers and farmers believes the ancient technology may be widely adaptable, enough that they will recreate a chinampa for their country’s pavilion at this year’s Architecture Biennale in Venice.

“Chinampas have a simple and intelligent design, created in a collective way that benefits not only people but all of the surrounding living beings, too,” said Lucio Usobiaga, a team member who has spent the last 15 years defending the remaining chinampas through a nonprofit he founded called Arca Tierra.

Mexico’s pavilion is a neat fit for the biennial’s main exhibition, “Intelligens. Natural. Artificial. Collective,” which is intended to show design projects that address climate change in creative ways. The chinampas are at once man-made and organic and can succeed only if there is cooperation among farmers, policymakers and the growing number of tourists who float through on popular canoe tours, gazing at fields of corn and flocks of egrets and pelicans.

Promoting the chinampa as an inspiration for eco-friendly design was an obvious choice for the biennale, team members said. “Venice is also built on water and has the same kind of vulnerabilities that Xochimilco has,” noted Ana Paula Ruiz Galindo, a founder of the design firm Pedro y Juana.

They pointed out that Venice and Xochimilco were added to the list of UNESCO World Heritage sites in the same year, 1987, and both places are island communities navigable by boats and working to balance the positive and negative aspects of tourism.

Venice has its iconic gondolas, while Xochimilco has its trajineras, flat-bottomed vessels, decorated in bright colors and fake flowers that take visitors on party-themed excursions. Both boats are operated by pilots who push them along channels using long poles.

As for how to recreate a chinampa on-site, that took some imagination. And compromise.

The Aztecs constructed their islands over time, using reeds and branches to make fences in the mucky lake bottom. These formed boundaries for multiple layers of sediment and decaying vegetation (and sometimes human sewerage) until the islands rose far enough above water to be farmed. In addition to growing crops like corn, beans and squash — using the traditional milpa agricultural method that naturally preserves nutrients in soil — they planted trees on the corners of the islands to stabilize the land.

Mexico’s pavilion, inside the biennale’s Arsenale complex, will feature a stripped-down version, much smaller than the 500 square meters (0.12 acres) of a typical chinampa. The exhibition will be enhanced by videos produced in Mexico City featuring real chinamperos, as the farmers are called, and bleachers will be installed along the walls. Artificial lighting will replace sunshine.

In the center will be a working garden planted with vegetables, flowers and medicinal herbs. (The crops were started in an Italian nursery and transferred to the Arsenale by boat in mid-April.) They will mature during the biennale, which continues through Nov. 23.

“By the end of the biennale, we will be able to harvest corn and make tortillas,” said Mr. Usobiaga. “Before that, we can harvest beans, squash, tomatoes and chiles.”

Visitors will learn about special seed cultivation techniques that are unique to chinampas and will have the chance to plant seedlings themselves.

In a nod to local agriculture, the chinampa will also employ a version of vite maritata, a practice established in ancient Etruscan agriculture that calls for planting grapes around trees, which serve as a natural trellis system for the vines. The exhibition team sees a link between the two forms of agro-forestry, combining trees and crops into one ecosystem.

“We are going to see this dialogue between two ancient cultures that both have a lot to say about how we can move forward,” Mr. Usobiaga said.

The exhibition team members said they wanted to be careful not to overly romanticize chinampas because they are not easy to duplicate on a scale that could feed a large population today. The farms work in Mexico City because they sit on a lake that lacks an outlet to another body of water, making water levels relatively easy to control. The opposite is true, of course, in Venice, which is on a lagoon close to the sea and always under threat from flooding.

Also, the economics of small farms — high production costs, low yields because of their size — make it difficult to turn a profit. Farmworker wages are generally too low to support people in urban areas, and the backbreaking work of planting and harvesting has lost prestige.

“This is a big problem here, that people, especially young people, don’t want to work the soil on chinampas anymore,” said María Marín de Buen, the team’s graphic designer.

Even in Xochimilco, many chinampas lie fallow because their owners cannot make a living. Some have been turned into soccer fields, which are rented out to the community; others are event venues where people celebrate weddings or birthday parties. Officially, the land is restricted from development, as well as from cattle grazing and the hunting of endangered animal species, though these things happen with alarming frequency.

Still, the team sees something inspirational at play: a connection between nature and the built environment, between existing water resources and the need to construct houses and schools. Architects who visit the biennale may not go on to design large swaths of farmland, but they can replicate the idea on a smaller scale using whatever conditions exist, said Jachen Schleich, a team member who is a principal of the Mexico City architectural firm Dellekamp + Schleich.

“Even if somebody does this in his backyard, he can at least feed his family, or the people on the four floors of his building, Mr. Schleich said. “It could be like a micro-intervention in the landscape or a public space.”

Public health officials in Los Angeles County have declared an outbreak of hepatitis A, a highly contagious liver infection driven by a virus that can, in rare cases, cause severe illness.

The condition, which is typically identified in fewer than 50 people in L.A. County each year, infected at least 138 people in 2024 and cases have remained unusually high so far in 2025. Officials say that levels of the virus in local wastewater suggest these figures are an undercount.

Here’s what to know.

How is hepatitis A transmitted?

The hepatitis A virus is spread through the so-called oral-fecal route, which means it is ingested through food or drinks that have been contaminated by microscopic bits of stool from an infected person. It can also spread through close contact with someone who is carrying the virus, even if they don’t show any symptoms.

Unhoused people are often at greater risk of contracting hepatitis A because they have limited access to proper toilets and hand-washing facilities. The virus is also more common among travelers to places with poor sanitation, men who have sex with men and people who use drugs.

But officials say many of the recent cases have occurred in people without those risk factors. They do not yet know why, but Dr. Timothy Brewer, an infectious disease physician and epidemiologist at U.C.L.A., said it had led him to worry about two things: food contamination, and community circulation.

“If you’re practicing good hygiene in a community that has access to potable water, you really should not be seeing a lot of this,” he said. “Something is going on — but exactly what that something is, we don’t yet know.”

What are the symptoms of a hepatitis A infection?

The first signs of the infection can look a lot like a classic stomach bug: fever, fatigue, nausea and a loss of appetite, followed by vomiting and diarrhea. Over time, people who become infected can also experience yellowed skin and eyes, dark urine and pale stools.

One of the challenges to halting a hepatitis A outbreak is that contact tracing can be nearly impossible. The infection can incubate for up to seven weeks before symptoms appear, and a person carrying the virus can spread it for up to two weeks before they feel ill.

In addition, a significant proportion of people who become infected don’t experience major symptoms, said Dr. Edward Jones-Lopez, an infectious disease specialist with Keck Medicine of the University of Southern California, so they do not visit their doctor, who in turn does not run a blood test and report the case.

Severe symptoms are most often seen in older adults, people with chronic liver conditions, and those with weakened immune systems or H.I.V. On rare occasions, a hepatitis A infection can be fatal. In this outbreak, at least seven people have died. That may seem like an unusually high fatality rate, but officials believe far more people have been infected than the official numbers show. Most have probably been asymptomatic, or shown symptoms mild enough to have been misidentified.

How is hepatitis A treated?

There is no specific antiviral medication for hepatitis A. The infection usually resolves on its own within a few weeks, and most people do not face lasting liver damage. But for some, hospitalization can be necessary.

In rare cases, the infection can devolve into an acute liver failure called fulminant hepatitis, which may require a transplant, said Dr. Jones-Lopez. “It can progress very, very quickly — that’s a very serious disease.”

If you think you might be infected, be sure to visit your doctor, drink lots of fluids, and get adequate rest.

How can I avoid it?

The best way to prevent a hepatitis A infection is through vaccination. The regimen — two doses of vaccine, at least six months apart — provides protection for life. It has been routinely given to children for the last two decades, but many adults 25 and older have not gotten the shots unless they were in a high-risk group.

The fact that the outbreak is occurring outside of traditional populations “underscores the need to reassess how — and where — we target prevention efforts,” said Dr. Anne Rimoin, an epidemiology professor at U.C.L.A., since “an infection anywhere is potentially an infection everywhere.”

If you are unvaccinated but know you have been exposed to a person carrying the virus, a prompt vaccination can prevent your becoming infected. Experts say that some people with weakened immune systems who are exposed could also benefit from receiving immune globulin as well. And good hygiene is a wise protective measure for everyone; wash your hands with soap and water, especially after using the bathroom, and before preparing food.