Studies by experts have found that human interference has upset the ecological balance of Chilavannur Lake. The water body is part of the Vembanad backwaters, a critically vulnerable coastal area according to a 2011 CRZ notification.
An assessment made by K.V. Thomas, scientist at the Centre for Earth Science Studies (CESS), and P. Harinarayanan, Scientific Officer at the Kerala State Council for Science Technology and Environment, found that the natural flow and tidal exchange in the lake had been restricted by artificial constructions, siltation and indiscriminate reclamation.
The Chilavannur Lake extends from Chettichira bridge on Subhash Chandra Bose road in Kochi Corporation to Irrigation bund road in Maradu Municipality.
It crosses Puthenpalam bridge on Sahodaran Ayyappan road and Chilavannur bridge on Chilavannoor bund road in the corporation limits. The lake is connected to the Vembanad through different canals and water bodies. At the north of Chettichira bridge, the lake narrows down into two small canals that flow further north.
“Sluices functioned as flow regulators at Chettichira, Puthenpalam and Chilavannoor bridges and at the Irrigation bund road at Maradu. These sluices were kept functional to support pokkali fields/filtration ponds where paddy cultivation and prawn culture were alternatively carried out depending on seasons earlier,” Mr. Thomas and Mr. Harinarayanan said.
Earlier there were no barriers to the natural flow and tidal exchange as filtration ponds required saline water, they said. Now with the disappearance of active pokkali fields/filtration ponds, the sluices have become non-functional causing siltation and blockade of flow. The entire lake had become stagnant threatening the health of the backwater.
Investigations revealed that large-scale reclamation of filtration ponds and tidal marshes had taken place on either bank along almost the entire stretch of the backwater. Reclamation is less near the Chettichira bridge in the north.
Most of the reclamation of filtration ponds and tidal marshes has taken place along the stretch from Puthempalam bridge area in the north up to the Irrigation bund road in the south.
Charles George, president of Kerala Matsyathozhilali Aikya Vedhi (TUCI), said fishing had come down in the lake following the drastic fall in fish in the ecosystem. “Pollution is the main reason for the decline in fish wealth here. The lake has become a dumping yard for sewage generated in the city,” he said.
Local residents allege that waste is being dumped directly in to the lake as the sewage treatment plant at Elamkulam, maintained by the Kerala Water Authority, has become defunct.
They said sewage from various parts of the city, supposed to be treated at the plant, reached the lake untreated.
However, senior officials of the sewerage sub-division of the KWA here rejected the allegations. They said the plant was functioning without any hiccups.