Bengaluru's Ulsoor Lake turns into fish graveyard: Is pollution plaguing water bodies?

Ulsoor Lake, a 50 hectare expanse of emerald green water in Bengaluru, is a lovely sight in spring when the trees lining it are blooming with the yellow of the tabebuia or covered in the purple of the jacaranda. But this spring, residents were greeted with the horrific sight of thousands of dead fish that had washed up on its shores early morning on March 7.

Photos and videos of the piles of fish went viral, provoking shock and calls for action, and various dignitaries visited the lake, from the local MLA, Roshan Baig, to the head of the state pollution control board, Lakshman.

Among those who visited the lake was Priyanka Jamwal, a fellow at Ashoka Trust for Research in Ecology and the Environment, who came to collect water samples, at the suggestion of a citizens’ group.




But while the tests showed that no chemical or poisonous substance had suddenly been released in the lake, the results should still concern the city’s residents. “We found that there was very high ammonia content in the water, which comes from untreated sewage and is toxic to the fish,” she says.

A Sip of Ammonia The dissolved oxygen in the lake had also decreased because of high temperatures during the day and the spread of algae, which was consuming the oxygen, reducing its availability for the fish. “These fish are not natural to the lake, they would have been released by the department of minor irrigation. The fish would have got very weak because of the ammonia,” says Jamwal, who studies water pollution.

TV Ramachandra of the Indian Institute of Science’s Centre for Ecological Sciences concurs that the depletion of dissolved oxygen in the water would have caused asphyxia in the fish. “At the inlet, the dissolved oxygen level was zero and in other parts of the lake, it was about 2 mg per litre. It should have been more than 5 mg per litre for the fish to survive,” he says. The sustained flow of untreated sewage, he says, was a major factor for the depletion of oxygen.

Bengaluru’s lakes, once admired for their unique, inter-connected design, which prevented flooding and recharged the groundwater, have of late been more in the news for its degradation.

Smoke on the Water Locals around Bellandur and Varthur lakes had got used to the sight of clouds of foam on the surface, but last year, high winds lifted the foul-smelling foam on to the roads. A few days later, parts of the foam caught fire. Ramachandra found that untreated sewage was again a major culprit, along with the presence of phosphorous, coming from indiscriminate use of detergents.

While a family on an average uses 1-1.5 kg of detergent a month, families in this region were using 4-5 kg on an average, he says. The phosphorous, along with untreated effluents in the lake and an accidental spark led to the fire, says a report by the Centre for Ecological Sciences.

Like the US, India should gradually move towards banning phosphates in detergents, which kills lakes, says Ramprasad V, a member of a citizens’ initiative to save the city’s lakes called Friends of Lakes. “We should begin by making detergent companies display the amount of phosphates they use, and gradually reduce it,” he says.

Groups like Friends of the Lake have made some progress in conservation, succeeding where the government hasn’t. Activities include cleaning the lake surroundings, keeping a check on the growth of algae and ensuring that sewage treatment plants are working. Such groups, believes Ramprasad, are the solution to the current crisis plaguing the lakes.

Jamwal, however, believes the civic agencies need to step in here. “The first thing is to have a sewage-treatment plant that will treat organic matter and convert ammonia into nitrate, which is not toxic for fish,” she says. At present, the city releases 1,400 million litres of untreated water every day, while sewage-treatment plants have the capacity to treat just 721 million litres. Of this, only 40-50% of installed capacity is being used, with the rest of the untreated water ending up in the lakes.

If untreated water keeps getting pumped into the lakes, it would soon contaminate groundwater resources, as is evident from the higher nitrate levels in the borewells in the vicinity of polluted lakes in Bengaluru, warns Ramachandra. Major health disasters like kidney failure would then be just a few sips away.