Photo courtesy of Chethika Gunasiri
Urban wetlands are the often overlooked ecosystems that sit, quite literally, between land and water on the margins of development and destruction.
In 2018, Colombo was named the world’s first Wetland City by the Ramsar Convention, an international treaty for the conservation of wetlands. Out of 18 cities that received the accreditation in the first round, Colombo was the only capital. While this recognition was a milestone, it also underscored the urgency of protecting what remains.
“Urbanisation has already destroyed about half of the wetlands in Colombo. And in developing countries like ours, the pressure continues,” said Dr. Chethika Gunasiri, a postdoctoral researcher at the University of Tokyo, who has spent over a decade studying and managing wetlands in Sri Lanka. Her career began at the Land Development Corporation where she was the very first environmental scientist in their newly formed Wetlands Management Division. Since then her work has bridged practice, research and advocacy, with a focus on using wetlands as nature-based solutions to urban challenges.
Wetlands are ecosystems that exist in the transition zone between land and water. They can be natural or man-made, freshwater or coastal, permanent or seasonal. Paddy fields, peatlands, marshes and mangroves fall under this broad category. Urban wetlands are those located in and around cities, suburban patches of green often mistaken for wastelands. “These wetlands are often the only green spaces left in city environments. They act as natural sponges, absorbing excess rainfall and preventing floods. They purify water, cool urban heat and provide habitat for urban biodiversity,” pointed out Dr. Gunasiri.
In densely populated areas like Colombo, where infrastructure has replaced much of the natural landscape, the services provided by these wetlands are vital. “They’re not just environmental assets. They are systems that sustain human life quietly and invisibly. Colombo is a naturally low lying area, located downstream of the Kelani River and adjacent to the coast. Historically, vast portions of the city were wetlands. Even areas like Colombo 7, now home to the BMICH, were once marshes,” Dr. Gunasiri said.
The transformation began during the British colonial period as the city was developed into a commercial port. The trend continued with post-independence urban expansion, particularly in the 1980s, when the administrative capital shifted to Sri Jayawardenapura Kotte. Marshes that once protected the Kotte Kingdom were drained and filled to make way for government buildings and residential neighbourhoods.
One of the least understood roles of wetlands is their capacity to combat climate change. “They are the world’s largest carbon sinks. Mangroves, for instance, can absorb up to three times more carbon than rainforests. Destroying wetlands not only removes this vital carbon absorbing function but also releases stored carbon into the atmosphere, exacerbating global warming. So we’re hitting ourselves from both sides – losing a carbon sink and releasing emissions,” Dr. Gunasiri said.
Urban wetlands also help cities adapt to climate change. They mitigate flood risk, purify wastewater and reduce the urban heat island effect. These are all nature-based solutions that are desperately needed as cities become hotter and wetter.
Despite their importance wetlands often go unrecognised and unprotected. “Most people don’t know that the marshland in their backyard is providing them with flood protection, clean air and water. Unlike places such as Sinharaja or Wilpattu, wetlands don’t have the same public awareness or visibility. This is why community engagement is so important. We can’t rely solely on government agencies. Local communities interact with wetlands daily, whether they realise it or not. They need to understand their value, report illegal dumping or filling and advocate for their protection,” Dr Gunasiri said, stressing that education was key. “If people are taught in school about the benefits of wetlands, how they’re part of the urban ecosystem, how they support life then they’re more likely to protect them.”
The threats to wetlands are many: pollution, encroachment, climate change and, perhaps most critically, invasive species. Sri Lanka’s wetlands are being overrun by plants such as water hyacinth and salvinia and fish species introduced through the aquarium trade. These invasives outcompete native species and drastically reduce biodiversity.
Another major challenge was institutional. Wetland ownership was fragmented across different government agencies with conflicting mandates. One agency may aim to conserve while another sees the land as available for development. This lack of coordination makes cohesive management difficult. “We don’t have a unified wetland policy or a single authority responsible for their protection. It’s a governance issue as much as it is an environmental one,” Dr. Gunasiri pointed out.
“We need to stop seeing wetlands as wastelands,” Dr. Gunasiri said. “They are vital infrastructures, just as important as roads, drainage or electricity. In fact, they often do the job better and without a power source.” Her work now focuses on quantifying these services and advocating for policies that integrate wetlands into urban planning. “If we’re serious about making cities liveable, sustainable, and resilient to climate change, then wetlands must be part of the blueprint.”