A community based initiative in Sri Lanka to keep our natural environment clean

Thalangama Wetland Watch

The Thalangama Area



Chetha Mithsuwi Jaykody from Rajarata University of Sri Lanka finished in December 2023 her final year research work (BSc) on “Anthropogenic impacts on Thalangama wetland in Sri Lanka” which she assessed though 50 semi-structured interviews at the lake and through field observations. The top two essential services of the wetland as perceived by the respondents were the supply of water for paddy cultivation (82% of respondents) and the provisions of habitats for plants and animals (70%). The main perceived anthropogenic threats included the dumping of household waste (74%) and release of wastewater (72%), as well as cutting of trees, fishing/hunting, unauthorized land usage and construction activities. Enhancing community awareness regarding the significance of wetlands and better collaborating between the various governmental and non-governmental organizations with a stake in the wetland was a key recommendation of the study.


Ranoja Dikowita, a student from the Department of Zoology and Environmental Management at the University of Kelaniya produced a Story Map about the Thalangama Lake for her externship related to the Nature Conservancy and National Geographic Society. The beautiful multimedia story involving aerial photographs can be found here Story map. To read the story scroll down after opening it.


Lashika P. Premarathne, undergraduate student at the University of Ruhuna, Dept of Geography, studied under the guidance of Mr. M. L Karunarathne the impact of anthropogenic activities on urban wetland and the potential of community conservation using the Thalangama lake and wetland as case study. The study was based on 50 questionnaire responses, 5 in-depth interviews, and secondary data. About 3 of 4 respondent consider the lake as a place of agricultural importance and recreation, but also see its ecosystem threatened by illegal waste disposal and land encroachment, influenced by political and social powers. While some problems, like animal road kills can be addressed, e.g., through wild life corridors, the overall conservation of this ecosystem requires a close collaboration between the government and the community.


Based on the environmental and economic impacts, the free-floating aquatic plant Salvinia molesta ranks a close second behind water hyacinth on a list of the world's most noxious and invasive aquatic weeds. For her biology class at the Overseas School of Colombo (OSC), Sheruni Pilapitiya studied how Salvinia, which is very common on the Thalangama lake, is reacting to changes of the lake’s water acidity or alkalinity, commonly measured via its pH (on a scale from 0-14). Sheruni used lake water and analysed Salvina biomass development under different artificially created pH scenarios (same temperature as at the lake). She identified in a well-designed experiment a pH of around 7 as optimal for Salvinia growth, which is within the common pH range (6.5-7.5) measured over the year in different parts of the lake.


In his personal project at the Overseas School of Colombo (OSC), Henry Edelman (Grade 10) studied during the summer of 2020 the biodiversity of the lake area to identify threatened species for which the Thalangama area is an important habitat and refuge to officially register it as a Key Biodiversity Area (KBA). KBAs are the most important places in the world for species to be safeguarded on our planet. Henry identified the endemic Western Purple-faced Leaf Monkey to match the selection criteria and posted a related proposal to the Regional Focal Point of the KBA Committee. Despite its endangered status, most villagers dislike these langurs which come in groups of around 20 and easily damage roofs and wires.


On 14th of August 2020, Malsi Angekumbura from the University of Kelaniya started her first sampling of water quality parameters in the Thalangama tank. The undergraduate research is being supervised by Dr Shamen P. Vidanage from the Department of Zoology and Environmental Management.


The Sri Lankan NGO ‘People To People Volunteers’ supports in the Thalangama lake area the conservation of bio-diversity with funding from UNDP GEF. One of their activities serves the promotion of organic vegetable cultivation on the bushy ‘highlands’ (ovita) within the paddy fields. Other activities support, for example, dairy farmers. The contact is Mr Anuradha Prabath Kumara.

People to People is supported by the University of Sri Jayewardenepura for water and soil sampling and analysis (BOD, EC, pH, Temp., nutrients, heavy metals, pathogens) under the leadership of Snr. Prof. Pathmalal M. Manage.


The “Nature Beyond the Horizon” environmental society of the Horizon campus is working on a regular bird monitoring as one of their activities. The contact is natbeho@horizoncampus.edu.lk


Mafaza Fara from Horizon Campus, Malabe, started in March 2019 her BSc research on water quality effects on fish diversity and distribution in Colombo wetlands, taking the Diyasaru park at Thalawathugoda, and the Thalangama lake as case studies. Aside water sampling and the analysis of water quality parameters, Mafaze will have to catch fish (with a net) and immediately release them back into the water after identification. Compared with the Diyasaru wetland, much fewer fish species were recorded in the Thalangama lake. “Tilapia” appears now the most common species which can live under certain oxygen conditions, and will be affected if the lake undergoes further maintenance measures that will decrease the already low dissolved oxygen levels in the water.


Nuwanthika Dharmaratne from the University of Colombo is studying water quality changes in five wetlands of Colombo, including the Thalangama Lake. One photo shows her and her team colleague in action, the other some of the aquatic macro invertebrates (snails, insects, etc.) which are bio-indicators for different levels of water quality. Nuwanthika is also looking at birds and dragonflies next to a set of chemical and physical water characteristics, as well as disturbance factors. She says: “I want to check the co-relations between all of these factors to determine those which could most closely reflect wetland quality”.


In 2016, Sudarshani Widanapathirana tried to assess the economic value of the Thalangama wetlands in terms of ecosystem goods and services based on household surveys, focus group discussions and field investigations for her Master’s Degree at the Open University, Nawala. The research revealed that the contribution of the wetland to the local community has an estimated annual value of LKR 29.4 million (ca. US$ 200,000 in 2016) or LKR 0.25 million per hectare and year. This value is mostly based on crop (78%) and livestock (11%) production. Looking at the total economic value, including indirect land use, the study estimated an annual value of 54.1 million LKR (US$ 360,000) or 0.46 million LKR (US$ 3000) per ha. This value is relatively high compared to other wetlands across the globe.

Source: www.ou.ac.lk


In 2011, Olivia Molden studied the perceptions of local residents of the Thalangama lake in view of the challenges the tank and wetlands are facing. Some of her results on what local residents value and which developments they dislike are presented in the section "Location and its challenges" Olivia showed among others differences in perceptions between residents who just moved to the lake and those living here longer. Interesting was also to see that of the residents, only 17% actually worked in the Thalangama area and another 18% nearby, while 14% work in Battaramulla, 35% in Colombo and 11% over an hour away. About 5% were retired. Olivia who lived for about 15 years in the Thalangama area interviewed 145 local residents for her B.A. study at Whitman College, USA.


Since many years, the Overseas School of Colombo (OSC) runs a very active outdoor learning and study program, led among others, by Ian Lockwood. Given the proximity of the Thalangama wetlands to the school, they are featured over the years in the OSC program (see https://ianlockwood.blog/tag/talangama-wetlands).

OSC worked at the lake collaboratively with the Field Ornithology Group of Sri Lanka (FOGSL). In 2005, OSC and FOGSL published a Field Guide for the Thalangama Wetlands which is out of print. For many years the school hosted an annual “Walk for the Wetlands” though this has regrettably not happened recently. In more recent years the students have been studying water quality in Thalangama.