‘Nanobubbles’ and tour boats could save an endangered Mexican wetland

Helmed by gondoliers, colorful tour boats known as trajineras, wend along a sun-dappled canal. They drift past serenading mariachi musicians in their own boats and vendors hawking snacks from wooden canoes.

This carnival-like scene plays out most weekends in Xochimilco (pronounced “zo-chee-MILK-oh”)—a UNESCO World Heritage site and a popular destination for tourists in southern Mexico City. Eleven percent of the country’s biodiversity can be found in this 6,400-acre wetland threaded by 105-miles of pre-Hispanic canals. It’s a fact few of the approximately two million tourists and chilangos (slang for Mexico City residents) who visit in a normal year know before boarding trajineras for an afternoon cruise.

But this fragile ecosystem faces an uncertain future, as pollution built up over decades squeezes life from these waterways, threatening a living heritage in the process.

In a surprising twist, Xochimilco’s trajinera tourists could be the wetland’s unlikely saviors, if a homegrown plan to use these wooden vessels to purify the canals’ murkiest depths, takes off.

An ecosystem in peril

Xochimilco’s wetland is regarded as one of the last living links to the Aztecs, thanks to the reserve’s remarkable floating farms known as chinampas . Humans built these islands—5,475 acres of them—from the nutrient-rich soil in the canal beds, making the chinampas one of the most productive types of agriculture in the world. In Mexico, they’ve been feeding the capital city for a millennium.

Today, some 55 tons of chinampa-grown vegetables—from beets to endemic crops such as talamayota squash—fill the trestle tables daily in...