Three hours of cleaning at Beddagana Wetland Park produced eight large bags of waste.
On 16 August 2026, our Field Programmes Coordinator, Amavin Mendis, led the first clean-up in a new monthly programme. He and Nisara were joined by five participants from the Sri Lanka Institute of Information Technology (SLIIT). The seven-person team worked along the boardwalk, through the butterfly garden, around the entrance, and beside the car park.
They separated everything they collected into PET bottles, glass bottles, and other non-biodegradable waste. Eight bags from a relatively small part of the park show how quickly discarded material accumulates in an urban wetland.
Why waste collects in urban wetlands
Beddagana does not sit apart from the city around it. Water reaches the wetland through a wider network of roads, drains and canals. During rainfall, these flows can carry bottles, polythene and other poorly managed waste into the habitat.
This connection to the surrounding waterways is also what makes Colombo’s wetlands so valuable. The Colombo Wetland Complex temporarily holds an estimated 39 per cent of the city’s stormwater before releasing it gradually, helping to reduce flooding (World Bank, 2018). However, when plastic enters this system, the same flows can carry it into wetlands or farther downstream. Research compiled by UNEP identifies small urban waterways as important routes for plastic pollution and recommends preventing street litter, improving waste collection and removing waste from waterways before it travels farther (UNEP, 2021).
Plastic pollution affects more than the appearance of a wetland. Larger objects can entangle or injure animals, while swallowed plastic may obstruct or damage the digestive tract. Sunlight, abrasion and weathering gradually break larger items into smaller fragments that are much harder to detect and remove. These particles can then enter freshwater food webs (UNEP/CMS, 2021).
Our own research at Beddagana and Diyasaru found plastic in fishing cat (Prionailurus viverrinus) scat, with the evidence suggesting that the cats acquired it through contaminated prey rather than by eating discarded waste directly. This shows how plastic entering an urban wetland may move through the food web and eventually reach a top predator (Ratnayaka et al., 2023).
What we found in fishing cat scat
My co-authors and I encountered this problem unexpectedly while studying the diet of fishing cats (Prionailurus viverrinus) in Colombo.
Between 2018 and 2021, we collected 276 fishing cat scat samples from Beddagana Wetland Park and Diyasaru Park. We were looking for prey remains, but we also found visible plastic debris larger than one millimetre in six samples, or 2.17% of the scats examined.
Laboratory analysis confirmed several polymers, including high-density polyethylene, polypropylene, polyester, and polyvinyl chloride. The material ranged from small fragments and fibres to part of a plastic shopping bag.
All six scats containing plastic also contained mammal remains. Some included remains from birds or freshwater fish. Fishing cats generally consume live or recently dead prey and are not known to forage in refuse. This suggests that the plastic may have moved through the wetland food web: prey consumed contaminated material, and fishing cats subsequently consumed that prey.
To our knowledge, this was the first published report of plastic ingestion by a wild felid. However, the study was designed to examine diet rather than quantify plastic pollution. Our methods could not reliably detect particles smaller than one millimetre, so the 2.17% occurrence should not be interpreted as a complete estimate of plastic exposure in Colombo’s fishing cats or wetlands. You can read the study here: Plastic ingestion by fishing cats suggests trophic transfer in urban wetlands.
Evidence from other freshwater predators suggests that our finding is part of a wider pattern. In South Wales, researchers found plastic in 50 per cent of regurgitated pellets and 45 per cent of faecal samples collected from Eurasian dippers (Cinclus cinclus). The birds feed mainly on aquatic invertebrates, and the researchers identified contaminated prey as the most plausible source of the plastic (D’Souza et al., 2020).
An Irish study detected microplastics in 57 per cent of 53 Eurasian otter (Lutra lutra) spraints. Fibres from the spraints resembled those previously found in brown trout (Salmo trutta) from the same catchment, again suggesting that the predator acquired plastic through its prey (O’Connor et al., 2022).
Plastic exposure has also been documented in other wetland predators. At Iran’s Anzali Wetland, northern pike (Esox lucius), the highest-trophic-level species examined, carried the greatest overall number of microplastics among the four aquatic species sampled. Many of these particles occurred in the gills, indicating that predators may encounter plastic directly from the water as well as through food (Saemi-Komsari et al., 2024). In central Florida, researchers detected microplastics in all 63 birds of prey examined, including ospreys (Pandion haliaetus) and red-shouldered hawks (Buteo lineatus) (Carlin et al., 2020).
These findings do not prove that plastic becomes more concentrated at each trophic level, or that every exposed animal experiences measurable harm. They do show that plastic has entered freshwater and wetland food webs far enough to reach predators. In some cases, the evidence points directly towards contaminated prey as the route of exposure.
Why keeping Colombo’s wetlands clean matters
Colombo was among the first 18 cities to receive Wetland City Accreditation from the Convention on Wetlands in 2018. It was also the first capital city to receive this recognition. The Colombo Wetland Complex supports more than 250 plant species and over 280 animal species, while its wetlands help regulate floods and cool the surrounding city (Convention on Wetlands, 2018; Convention on Wetlands briefing note).
Colombo’s recognition as a Wetland City is something to be proud of. That pride should be visible in how we treat these habitats. Our monthly clean-ups will remove waste that has already reached the wetlands, but keeping new waste out of drains and waterways is just as important.
Under Amavin’s coordination, wetland clean-ups will now form a monthly part of our field programme, beginning at Beddagana. We will announce the date of our next clean-up soon. If you would like to help care for Colombo’s urban wetlands, join us.
