Following the heavy downpour last week, waves breaking on beaches in Chennai have turned black, which has evoked reactions that have ranged from panic to revulsion.
On Saturday, a number of visitors to the beaches, including Marina, Foreshore Estate, Eliotts and Thiruvanmiyur, reported that the sea had changed colour.
Visitors to these beaches on Saturday stayed away from the sea.
“This seems unusual. We have never observed the seawater taking on such a colour, at the Thiruvanmiyur beach,” said Pranav Vijay Sekar, an Anna University student who visited the beach on Saturday.
J. Savarinathan, a fisherman from Dommingkuppam, said such occurrences have happened during severe cyclones in the past.
“We do not venture into the sea for fishing during such periods. The smell is also bad,” he said.
Researchers in Chennai offered a wide range of explanations for this phenomenon, some of the citing research papers from the past.
“The reason for the sudden change in colour of the seawater can be identified only after a proper study,” said R. Ramesh, Director, National Centre for Sustainable Coastal Management.
“We will look at the satellite imagery to find the reason. The wave height has increased because of the depression. This could have churned the sludge blocked near the mouth of Cooum and Adyar rivers. The sediments in the continental shelf located close to the shoreline could also have contributed to the colour change,” said Prof. Ramesh.
E. Vivekanandan, consultant, Central Marine Fisheries Research Institute (CMFRI), said the amount of sewage mixing in the rivers could be high.
“A lot of sewage is being pumped into the rivers in the city. That can be a reason. Normally, during the rainy season there is a chance that seawater could be black because of the reflection of the sky. Another reason is the churning of water because of high wind. The bottom water would churn and absorption of light will be affected. Due to turbidity, the light reflection could have caused the dark colour. The water has to be analysed. If it is sewage, the oxygen content would be low.”
Chennai Metrowater officials said 900 million litres a day (mld) of sewage had been conveyed to waterways through sewer pipeleines on Friday as against 500 mld.
“Entire rainwater load was carried in sewer pipelines covering 3,600 km. The stormwater network of Chennai Corporation was inadequate,” said an official.
(With additional reporting by Deepa H. Ramakrishnan and K. Lakshmi)