This is one area where environmentalists turn red when you say green. What has got their goat is the waters of the Powai lake turning green, thanks to the blue green algae in the waterbody.Their presence is not a good sign, they say. An algal bloom indicates increasing quantity of sewage in the lake. If they are not cleared, the lake will soon turn into a mass grave of fishes.Not just to fishes, the algae pose a threat to humans as well. “Studies have shown that they can be harmful to the skin of people coming into contact with the water and to animals drinking from such waterbodies,” said Dr Pramod Salaskar, who has done a study on Powai lake.<!– /11440465/Dna_Article_Middle_300x250_BTF –>”During my recent visit to Powai lake, the water seemed completely green. In fact, the water was appearing so green close to the banks as if someone has added colour on it,” said Sunish Subramanian, secretary, Plants and Animals Welfare Society (PAWS), Mumbai. Subramanian had recently filed a complaint against the Brihanmumbai Municipal Corporation for releasing drainage water into the lake.Maharashtra State Angling Association (MSAA) members say that they are preparing an exhaustive report on the algal bloom and will submit it to the BMC. “The blue green algae have increased, and, in fact, our members have seen fishes coming to the surface early in the morning to breathe. This only shows that the algal bloom is reducing the oxygen level in the lake,” said Gordon Rodricks, vice-president of MSAA. MSSA members have removed large quantities of green algae sludge from the lake several times this month, he said.Rakesh Kumar, chief scientist, National Environmental Engineering and Research Institute (NEERI), said that the green effect is “obviously due to the sewage water, which contains nutrients like nitrogen and phosphates. As they enter the water, they lead to an algal bloom. With the presence of such high quantity of nutrients and water receding due to summer, the situation will only worsen,” he said.Salaskar said that fishes are dying and already floating on the lake surface. “The blue green algae reproduce very quickly and they are not only known to deplete the dissolved oxygen levels of water, especially during early morning, but also increase toxicity,” he said.Salaskar, who met BMC officials on Tuesday, requested them to keep all aerators operational in the night as well as early morning so that dissolved oxygen level becomes normal during early hours for the fish.According to sources, the 17 floodgates installed to stop sewage water from entering the lake are completely ineffective. Also, of the six aerators in the lake, only a couple actually work.Dr Masahisa Nakamura, chairman of the International Lake Environment Committee (ILEC), Japan, spent several hours studying the Powai lake on Tuesday with MSAA members and Salaskar, secretary of Naushad Ali Sarovar Samvardhini.”Be it Powai lake or any other waterbody., the problem is due to the stress on it from various quarters, including sewage. Reducing this stress is the only solution and it cannot happen by blaming the municipality, community or the government. It calls for a complete involvement of all stakeholders,” he said.”Pollution in Powai lake is not new and it could take years to clean it, but it is important that we start taking steps,” he said.