A lake ecosystem gasping for breath

A recent episode of fish kill in Ashtamudi Lake has once again brought to the fore the life-threatening issues of sewage contamination, plastic pollution, encroachments, and uncontrolled weed growth stifling the vital lake ecosystem, a protected site of international importance. Navamy Sudhish traces the reasons for the lake’s ill health, which is deteriorating each day

In the last week of October, Thambi, 58, a resident of Kadavur in Kollam, was returning from work when he found several dead fish floating near the banks of Ashtamudi Lake.

At first, he thought they were remnants of fishing with explosives and poison, locally known as ‘thotta’ and ‘nanchu‘, illegal practices still rampant in many parts of the lake that is spread over 5,700 hectares. It was designated by the Union Ministry of Environment, Forests and Climate Change (MoEFCC) as a Wetland of International Importance under the Ramsar Convention in 2002.  

As Thambi took a hard look at the waterbody, he noticed species such as pearl spot and tilapia scattered over. It set the alarm bells ringing. “I felt a sense of foreboding as it was nothing like the sporadic deaths we have seen over the years,” says Thambi. 

By next morning, the Kuthirakadavu area of the lake was covered with a thick carpet of dead fish leaving a strong stench in the air. While the visuals of the fish kill went viral on social media and experts arrived to collect samples, the people living near the waterbody had no doubts about the cause. “They can no longer fool us with scientific mumbo jumbo as we know very well what led to the mass death of fish. Relentless discharge of effluents into the lake has made its water toxic,” says R. Girija, a resident and homemaker. Her neighbour Rajani echoes her sentiment and says, “everything, including septage and plastic waste, ends up in the lake. If you have any doubts, check the parts where the water is so slimy, and the colour is nearly black“.  

According to a preliminary report submitted by the Kerala University of Fisheries and Ocean Studies (Kufos), the mass mortality event was caused by an algal bloom, a phenomenon that occurs due to an overload of nutrients. The proliferation of algae leads to oxygen depletion in water suffocating aquatic organisms. The study also found the presence of streptococci and E. coli in water pointing to sewage contamination in Ashtamudi.

While there has been consistent dumping of plastic, poultry waste, and abattoir waste, sewage lines from many households also open to the lake. In July 2024, the Kerala High Court had directed the Kollam district administration to remove illegal encroachments in and around the waterbody and take immediate steps to prevent waste and effluents from polluting the Ramsar site. “It is high time that we need to secure this kayal poramboke for future generations and also ensure free flow of water in Ashtamudi Lake,” the court had observed. 

A study by the Department of Aquatic Biology and Fisheries, University of Kerala, revealed dangerous levels of microplastic pollution in the aquatic ecosystem of Ashtamudi Lake. The presence of microplastics was detected in fish, shellfish, sediment, and water samples with the highest percentage found in macrofauna at 60.6%, fish at 19.6%, and shellfish at 40.9%. While MP (microplastic) types detected are fibres, fragments, and films, the study also identified the presence of a range of polymers, including nylon and polypropylene.  

The analysis found five polymers from shellfish, five from fish guts, four in sediment, and four in water samples. According to the study, the existence of these plastic polymers and heavy metals, including barium and iron in samples, poses a threat to vulnerable biota.

“This investigation of MPs in Ashtamudi Lake highlights the system’s susceptibility to plastic pollution and the bioavailability of smaller MPs to aquatic organisms,” says the study. The lake’s fringes are used as dumping grounds for municipal solid waste, a primary source of plastic pollution in the aquatic ecosystem. Key sources of microplastics in the lake include fishing and aquaculture activities, untreated sewage, unscientific solid waste management in lake watersheds, and unsustainable tourism practices. The National Green Tribunal (NGT) had taken a suo motu case on microplastic pollution in Ashtamudi Lake based on the study. 

Later, the Central Pollution Control Board (CPCB) reported that the water quality data at four locations of the lake were non-complying with respect to Primary Water Quality Criteria for Bathing notified under The Environment (Protection) Rules, 1986. “Algal blooms may be a natural phenomenon but anthropogenic stressors, especially land-based activities, can significantly amplify their frequency and intensity. The presence of harmful substances like heavy metals in fish tissues can affect public health through consumption. Also, the neurotoxins in harmful algal blooms may impact animal and human health. So, implementing proper waste management measures and sustainable practices are integral to protect waterbodies like Ashtamudi Lake and prevent future fish kills,” says A. Bijukumar, Professor and Head of the Department, Department of Aquatic Biology and Fisheries, University of Kerala.

An earlier survey conducted by the Kerala State Pollution Control Board (PCB) had indicated that the lake was under pollution stress due to indiscriminate discharge of sewage and dumping of solid waste from households and establishments. It was also revealed that numerous drainage channels laden with waste empty into the lake at the southern end. The survey was carried out in Kollam Corporation and the grama panchayats of Perinad, West Kallada, East Kallada, Munroe Thuruth, Panayam, Kundara, Thrikkaruva, Thevalakkara, Thekkumbhagam, Chavara, and Neendakara.  

As per the survey, 65% of the residents dispose of their sewage through septic tanks and soak pits, 15% use toilet pits, and 18% of residents dispose of directly into the lake. Yards operating illegally and houseboat operators, who do notadhere to responsible waste management practices, also aggravate the problem.

Following an intervention of the Environment Committee of the Kerala Legislative Assembly, panchayats along the borders of the lake were asked to prepare projects on a war footing to ensure proper waste management. The local self-government institutions  concerned were asked to construct sewage plants for treating waste and ensure all houses near the lake have septic tanks. It was recommended to set up floating septic tanks in Munroe Thuruthu, a group of inland islands, with the help of modern technology, and strengthen surveillance measures to prevent septage, abattoir, and houseboat waste from reaching the lake.

“Though instructions and guidelines have been issued multiple times, discharge of septage waste continues in many parts. While some houses were sanctioned biotoilets, there are still many houses that lack proper septage management facilities,” says a senior official from the Fisheries department.

While the Kollam Corporation had launched several programmes, including the ambitious ‘Jeevananu Ashtamudi Jeevikkanam Ashtamudi‘ [Ashtamudi is life, Ashtamudi should live], to protect the Ramsar site and restore its biodiversity, they all lost steam in the absence of consistent follow-ups.

“We had made allocations for getting rid of all outlets from the houses to Ashtamudi Lake and providing free biodigester toilets to the BPL families. Scientists say the recent fish kill in Ashtamudi lake is a natural phenomenon. While pollution levels have considerably decreased compared to the past, the Corporation remains committed to keeping the lake clean. Since the launch of ‘Jeevananu Ashtamudi Jeevikkanam Ashtamudi’, 160 tonnes of plastic has been removed from the lake, with 120 tonnes already handed over to Clean Kerala Company Limited. Additionally, a sewage treatment plant (STP) which can process 500 tanks of sewage waste a day has been completed, though the connecting pipelines are yet to be installed,” says Mayor Prasanna Earnest.

Meanwhile, inland fishers, the frontline victims of aquatic contamination, say they have been witnessing the changes in the estuarine ecosystem for a while. “There are around 17 canals and channels from the estuary, but right now, they are full of sediments and debris. Lack of flow has affected the ecosystem, and many parts need dredging. Some 15 years back freshwater prawns from Ashtamudi contributed 12% of total exports from the State. Now it has diminished to less than 5% while many species have gone extinct. Sediment build-up is a serious issue affecting the health of the waterbody and the livelihood of thousands of fishers,” says Henry, a fisherman.  

At the same time, fishers from the Dalavapuram area are facing another challenge as water hyacinth is spreading in the area and making it impossible to cast their nets in areas covered with the invasive aquatic plant. “This rapidly spreading plant limits our fishing area and often damages our gear,” Babu, a clam collector. He says the algal bloom had a devastating impact on their livelihood and many cage farmers also suffered huge losses.  

“There were no takers for fish for several days and even now regular customers are refusing to buy from us. Cage farmers lost thousands of ready-to-harvest fish in a single day,” he says.  

Xavi, a fisher from Thekkumbhagam, says the authorities are doing nothing for the long-term health of the lake. “We have watched many species vanish from the backwater and the size of some varieties, including the Kanjirode pearl spot which is said to be the most delectable, is shrinking. Random clean-up drives will not suffice, as we need consistent efforts,” he says. 

While fishers have been complaining about low yields for the past few years, scientific studies point to habitat degradation and the rise in anthropogenic disturbances. “Septic tanks and wastewater pipes from most households on the bank open to the lake and this is no secret. Encroachments are also common and a cruise through the backwaters will prove these are not mere allegations. Just look at the volume of waste washed ashore next to the Kollam KSRTC stand in the heart of the city. If this continues, the lake will be beyond redemption very soon,” says Jackson Neendakara, district secretary of the Matsyathozhilali Congress

Published - November 21, 2024 08:03 pm IST