Thursday, October 30, 2008

Sewage kills hundreds of fish in Siddapura lake

Sewage kills hundreds of fish in Siddapura lake

Bangalore: All it takes is one look — at the Siddapura lake, near Marathahalli — for an understanding on the standards of maintenance of lakes in Bangalore, once identified with sparkling waterbodies. On Wednesday morning, hundreds of dead fish surfaced on the lake, causing a pungent stench in the neighbourhood.
R Manjunatha, a fisherman, had taken the lake on contract from the Fisheries Department to cultivate ‘katla’, a variety of fish. He was shocked to see the dead fish in the morning and said it was a huge loss — of over Rs 50,000 — for him. Local farmers and residents said a pipeline connected to BEML Layout carries sewage into the tank every day. An excess of sewage inflow could have been the reason behind the deaths, they pointed out.
Manjunatha had taken the lake on contract from the fisheries department three years ago. He pays the government Rs 3,800 every year to cultivate fish in the lake. “All the sewage from the neighbouring BEML Layout is directed into the lake through a pipe. The fish must have died due to the sewage being dumped into the lake. It’s a big loss for me. I don’t know what to do. Even the fish that are left might die gradually,’’ Manjunatha said.
According to former environment secretary and conservationist A N Yellappa Reddy, what leads to most of such cases is the reduction in the dissolved oxygen (DO) level in the water. “If the Chemical Oxygen Demand (COD) is very high due to the concentration of effluents or of sewage, the DO level comes down. If the DO level is lower than 2 mg, the fish can’t survive. The tank is a living entity where a number of micro-organisms thrive. The oxygen levels need to be optimal for their survival,’’ he said.
Such cases usually occur when untreated sewage or chemical waste is let into the waterbodies. Sudhira, a researcher at the Indian Institute of Science (IISc) who has done extensive research on Bangalore’s lakes, says though there are treatment plants in the city, the sewage-collection process is not up to the mark. “A lot of untreated sewage, hospital waste and chemical effluents are discharged into the tanks through storm water drains. The lakes need to have cascades falling into them from a high point, helping air-water interaction and keeping the oxygen levels high,’’ he explains. Further, adequate micro-organisms like algae are required to sustain life in the water.
There are four big water-treatment plants in the city and a few small ones, but the numbers are proving to be alarmingly inadequate.
Similar incidents in the city
Thousands of dead fish surfaced on Puttenahalli lake in June 2005. The authorities identified sewage discharge into the lake as the cause. The same problem was seen in Ulsoor lake in January and Vangiana lake in May, the same year.
A variety of fishes died in the Lalbagh tank just after the flower show in 2007. The authorities identified that the visitors to the park had littered the tank with food, plastic and other waste.
Almost a year ago, Varthur lake had developed froth because of the soap and detergent waste, leading to fish deaths.
Probable reasons behind the fish death, according to Sudhira
Drop in DO (Dissolved Oxygen) level
Inflow of sewage with a lot of organic matter
Increase in algal bloom
Eutrophication (increase in chemical nutrients, typically compounds containing nitrogen and phosphorous, in an ecosystem)


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