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Water degradation of Diyawanna Oya: Declining water quality in urban areas  

18 Apr 2021

  • First the Kelani River and now Diyawanna Oya 

By Yumiko Perera    A significant decline in the water quality of the Diyawanna Oya has drawn attention to the degradation and declining quality of water in urban water bodies.  As pointed out by Opposition Leader Sajith Premadasa in Parliament recently, the waters of the Diyawanna seem discoloured, and green sediments of algal bloom can be seen spread throughout the lake.  According to Premadasa, drains and sewerage systems from homes around the area have allegedly been diverted to the Diyawanna Oya, which surrounds the Parliament.  Diyawanna Oya, an important recreational site in the greater Colombo area which is prone to severe threats from illegal reclamation and constructions for urban development purposes, is known to be home to a rich habitat of indigenous flora and fauna.  Making a significant contribution towards the social wellbeing of the urban and suburban society in the vicinity, the Diyawanna Oya wetland ecosystem is also considered to be an important flood retention area.  Although the Central Environmental Authority (CEA), as instructed by the Minister of Environment Mahinda Amaraweera, is yet to submit an immediate environmental report on the water pollution of the Diyawanna Oya, according to the Minister of Environment, the water pollution in the Diyawanna Oya had not been as severe as it is at present.  CEA Chairman Siripala Amarasinghe, speaking to The Sunday Morning, stated: “We have identified that the main reason for the discolouration of the water in the Diyawanna Oya is a type of algae, which has caused algal blooms across the lake, resulting in murky discoloured water.”  Consisting of both natural and man-made habitats including freshwater marshes, streams, lakes, and canals, not only is the Diyawanna Oya ecosystem home to a large number of species of fish including a variety of endemic species, but is also well-populated with aquatic birds, both local and migratory.  According to Amarasinghe, algal blooms are not an uncommon occurrence in the Diyawanna. “The water in the Diyawanna Oya has been collected in one place and is stagnant. Algal blooms such as this are quite a common occurrence. It’s not something we haven’t seen before. While the algae blooms have not spread up to the extent where the eco life would be affected by it, it is most certainly our responsibility to look into the matter and come up with a solution to address this issue adequately,” Amarasinghe said.  Water quality is vital to maintain healthy aquatic ecosystems, especially when it comes to wetland ecosystems. As river flow slows down, and wetlands dry out, nutrients become concentrated, feeding massive blooms of algae.  Algae are known to thrive in warm weather, proliferating and spreading across stagnant waters. Algal blooms and sediments cloud the water, cutting out light to organisms below. Starved of sunlight, animals and plants begin to die, and eventually, so do the algae. The decay consumes oxygen, an element essential to aquatic organisms.  While the rapid growth of population and increase of urban activities pose a significant threat to urban water bodies, Amarasinghe revealed that a special team has been deployed to monitor waste being released into the Diyawanna through sewerage systems.  “Wastewater and other effluents from the houses in the vicinity are being released into the waters of the Diyawanna. More often than not, the release of wastewater into the Diyawanna is done through illegal methods. There have been instances where we have found underground pipelines being used for this purpose too. Most of these activities happen in the dead of the night,” revealed Amarasinghe.  The Diyawanna ecosystem provides a livelihood for some of the people living in the area. While a small fraction of the population depends on fisheries and uses cast nets, fishing rods, and occasionally other types of traps to catch both ornamental and edible fish, the recent development along the wetland ecosystem plays a pivotal role within the suburban communities in the society. Under these circumstances, it is imperative to take necessary legal measures against the people that pollute the waters of this invaluable wetland ecosystem.  Stating that necessary legal measures would be taken against people who release waste material into the waters of the Diyawanna, Amarasinghe further added: “We are looking into the matter. We are working on the report and it will be presented at the Parliament soon.”  Speaking on the measures taken to address the declining quality of water in water bodies across the island, Director of the Environmental Pollution Control Unit, Central Environment Authority Dr. Sanjaya Rathnayaka, speaking with The Sunday Morning said, “After inspecting 10,410 locations and sources that pollute the 103 rivers across the country, we have managed to identify certain issues that contribute to the pollution of these water sources. This was done through a survey that spanned over two weeks.”  “‘Surakimu Ganga’ addresses a variety of issues in coordination with the necessary authorities in question. The program aims to clean rivers and water sources all across Sri Lanka through a systematic plan,” Dr. Rathnayaka added.  “If you look at the Kelani river, we have taken action against at least 95% especially when it comes to controlling industrial waste being released into the river. Domestic wastewater being released into the rivers is harder to control. There are so many illegal construction sites and houses along the banks of the river, and I feel that this is something local government institutions should pay special attention to. Through the ‘Surakimu Ganga’ initiative, all of these institutions are brought together, and they work in coordination to control the degradation of the water sources across the country,” observed Dr. Rathnayaka.  Through an audit carried out by the Environmental Audit Unit of the Auditor General’s Department, it has been revealed that the Kelani River is increasingly polluted. Approximately 80% of the water supply used within the city of Colombo, as well as its suburbs is supplied by the Kelani river.  Sharing his view on the declining water quality of the Diyawanna Oya, Dr. Rathnayaka elaborated, “The sewers are the issue because even if the water is treated the levels of the nitrogen phosphorous in the water would remain, and that is the main reason for the growth of algae. Especially in a stagnated water body, this is common given that there isn’t much flow. When domestic waste gets into the water, the concentration of nitrogen phosphorus rises and that is what has happened to the Diyawanna.”  A variety of environmental goods and services have been bestowed upon us so generously by these water bodies, making them more vulnerable to human exploitation. Human activities have resulted in the alternation of these habitats, and various industrial effluents being released into these waters has brought along devastating consequences to ecosystems surrounding water bodies such as the Diyawanna Oya.  Nayanaka Ranwella, environmentalist and environmental activist, speaking with The Sunday Morning shared, “There are several issues when it comes to the Diyawanna Oya. There are several auto detailing outlets that operate within the vicinity of the Diyawanna Oya. The wastewater which includes lubricant oils gets released into the waters of the Diyawanna without being purified.  Apart from that, there are various invasive plants like ‘Japan Jabara’ that are quite prominent in the area, resulting in a lower level of oxygen in the water, and posing a huge threat to the ecosystem. The water then becomes stagnant and the organisms that depend on the waters slowly start dying.  The riverine forests that once filtered the waters of the Diyawanna naturally, no longer exist thanks to human settlements and mushrooming development projects in the area,” Ranwella concluded.  Non-regulation of human activities, along with the negligence of the authorities have been identified as reasons as to why the quality of water within Colombo and its suburbs continues to deteriorate.


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