The Hindu

Monsoon effect

- ALOYSIUS XAVIER LOPEZ (With additional reporting by Deepa H. Ramakrishn­an and K. Lakshmi)

Seawater turned black in colour after the onset of north east monsoon in Chennai. A scene at Pattinapak­kam beach.

CHENNAI: Following the heavy downpour last week, waves breaking on beaches in Chennai have turned black, evoking reactions ranging from panic to revulsion.

On Saturday, a number of visitors to the beaches, including Marina, Foreshore Estate, Elliots and Thiruvanmi­yur, reported that the sea had changed colour.

Visitors stayed away from the sea. “This is unusual. We have never observed the seawater taking on such a colour,” said Pranav Vijay Sekar, an Anna University student, who visited the Thiruvanmi­yur beach on Saturday.

J. Savarinath­an, a fisherman from Dommingkup­pam, however said such instances had occurred during severe cyclones in the past.

“We do not venture into the sea for fishing during such periods. The water smells bad too,” he said.

Researcher­s in Chennai offered a wide range of explanatio­ns for this phenomenon, some of the citing papers from the past.

“The reason for the sudden change in colour of the seawater can be identified only after 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,” he added.

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.

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