Lakes and wetlands are welcome natural oases amidst the concrete and asphalt of the urban world. In many cities, they are magnets for people seeking a chance to go birdwatching, fishing, swimming, or just use the water as a scenic backdrop.
But these spots have an invisible and unappetizing side as well. They can be hotspots of antibiotic-resistant microbes, posing a potential health risk to people coming in contact with the water. A survey of wetlands in Chinese cities discovered levels of these microbes on par with untreated sewage, Chinese scientists reported last week in Nature Cities.
The discovery highlights the overlooked risks of what are commonly seen as urban amenities. It also points to possible ways to clean up these waterways. Rather than being a “regulatory blind spot,” these waterbodies “should serve as ‘frontline outposts’ guarding public health and ecological security, requiring our concerted efforts to ensure they serve city residents safely,” lead author Da Lin of the Chinese Academy of Sciences’ Institute of Urban Environment wrote in an online essay discussing the research.
The scientists were first alerted to the possible problem while strolling past a wetland in a city park “bustling with human activity,” Lin wrote. While such waterbodies might look appealing, they can also serve as impromptu stormwater storage ponds, capturing runoff from nearby streets or even from overflowing sewage pipes. The scientists wondered to what degree that also turned them into magnets for antibiotic resistant bacteria, which are known to flourish in urban settings.
They collected water samples from 17 wetlands in 9 Chinese cities, filtered the water and examined the DNA left in the filters to see what viruses and bacteria were present, and whether their genes contained signs of antibiotic resistance.
The test revealed nearly 750 types of genes coded for antibiotic resistance in concentrations 9 times greater than what researchers have found in natural lakes. It was approximately the same contamination levels seen in tests of raw sewage, and roughly four times the average levels found in urban wetland elsewhere in the world, based on results from other studies.
This microbial stew included genes for resistance to sulfonamide and tetracycline, as well as genes for broader resistance to a range of antibiotics. The scientists also found traces of 67 different microbes known to infect humans, particularly from the Pseudomonas genus, which are known for having antibiotic resistance. “This data objectively demonstrates that urban wetlands have become important reservoirs” for antibiotic resistant genes, Lin wrote.
Not all wetlands were equally problematic. Waterbodies in poorer cities had higher levels of contamination with antibiotic resistant bacteria. That might be linked to weaker urban infrastructure, which enables more untreated stormwater to flow into these lakes and ponds, the scientists wrote.
That also points to possible ways to tackle the problem. A number of Chinese cities, including the capital of Beijing, have in recent years begun building nature-inspired infrastructure to better cope with stormwater. These so-called “sponge cities” use tools such as permeable pavement, landscaping engineered to soak up rainwater and, yes, wetlands meant to clean the water.
While such infrastructure can help, as the new research points out it can also create public health headaches.
To guard against these wetlands becoming more problem than solution, the scientists called for more robust monitoring and regulation of these waterbodies. Among the recommendations: Set standards for contamination levels with antibiotic resistant bacteria; create a list of high-risk wetlands; and keep the antibiotic problem in mind when designing and managing urban water spots, rather than focusing only on removing nutrients such as nitrogen and phosphorous, which can spark algae blooms.
Just as public beaches are now sometimes closed when water tests show high levels of E. coli, perhaps one day something similar might be in place for high levels of antibiotic resistance.
Lin, et. al. “Urban wetlands as hotspots of antibiotic resistomes and their potential viral transmission.” Nature Cities. April 17, 2026.
Photo by LUM3N/Freerange Stock
