Green Lake

Those who visit Puttenahalli lake these days would see almost the entire surface green with algae.

On researching about algae, we found this information on an algae control program webpage.  

Algae grow when they have the right conditions such as adequate nutrients (mostly phosphorus but nitrogen is important too), light levels, pH, temperature, etc. Generally the amount of phosphorus controls the amount of algae found in a freshwater lake or water body. The more nutrient-enriched a lake, typically the more algae in the lake. 

Healthy lakes need algae. Algae are important to the productivity of a lake or water body. Algae are primary producers. They use sunlight (through photosynthesis) to produce carbohydrates and are eaten by grazers such as protozoa and zooplankton (little animals like water fleas and rotifers). The zooplankton are, in turn, grazed upon by fish, which are eaten by bigger fish, and on up the food chain. A productive lake produces large fish and good fishing for humans as well as supporting food and habitat for wildlife and waterfowl. In this context most algae are desirable for lakes.

While algae are beneficial, there are some algae that are less desirous than others, and we’ve been worried about the green on the lake’s surface. We will need to take out samples of the algae to check the type. Experts in the field whom we got in touch with tell us that "it is some kind of seasonal algae that is blooming now. Even though there is no sewage entering the lake, there are lots of previously collected nutrients within the lake that can equally well support such seasonal blooms." They also say that using algaecide to control the growth will have short term effect while adversely affecting the natural flora and fauna of the lake ecosystem. 

The only real solution seems to be to have more clean rain water entering the lake and diluting the nutrient residue. Unfortunately, the monsoon has been very bad this year and in the few showers that we did have, only the inlet near the coconut grove let in water. Unlike last year, only excess surface water from South City reached the lake. We need to find out if L & T has blocked the storm water drainage in some way and are diverting the rain water into the underground sewage line. If this is corrected and rain water from South City let into the lake, the level will increase considerably whenever it rains.

Another hope is that the BBMP is expected to begin work on the diversion channel from Brigade Millennium arch shortly. Of course, if the rain gods continue to overwhelm other parts of the country and not Bangalore, we can do nothing but watch the algae take over the lake completely. While it is no consolation, another expert told us, "Why only your lake? All the lakes in Bangalore are green now because of less than normal monsoon!"   

Inputs and photo: Usha Rajagopalan


  1. Arathi Manay Yajaman says:

    There is a new informal group that has been formed to save Bangalore lakes Arbind Gupta (from ANIT) is moderating it. We hope that through this group, people like you who are looking to protect the lakes in their vicinity will find it easier to do so.
    With regard to encroachments, one can complain to BMTF, the concerned Govt agencies and / or tahasildar. Follow up and persistence is critical because very often the local administration is aware of the encroachments but ignore them for various reasons. You could also file an RTI with the concerned Govt agency to establish the lake boundary. See the FAQs on PNLIT’s website

  2. Karthick Bala says:

    I am Karthick Bala and I am studying algae of Indian subcontinent since 2004. I would like to bring some points related to algae in Bangalore lakes.

    1. There are 1000s of species of algae growing in freshwater bodies of subcontinent and each species have its own specific niche (preferable environment). Some species grow only in high nutrient level or high pH and some species on lower side. Researchers take advantage of this characteristic feature to use algae as a “bioindicator”. If one can get a list of species of algae, then we can ascertain the pollution status of that water body.

    2. Under certain conditions, one kind of algae can take control of whole lake/pond. This is caused by high amount of nutrient input (N/P) into the water body, which is also called as “Eutrophication” and result in algal bloom. Most of the Bangalore lakes are very close to this condition or already in eutrophic state. One of the common bloom forming algae in Bangalore lakes are “Microcystis” – a notorious blue green algae known for growing in nutrient rich conditions and inhibit the growth of other algae, so it affects the diversity of invertebrates and so on along the food chain. When the cells of Microcystis die, they release a chemical called “microcystin”, which is toxic to other life forms; even for humans it can cause skin irritations.

  3. Karthick Bala says:

    3. Based on the lake characteristics (physical and chemical) algal diversity varies. In Bangalore by polluting lakes we have lost diverse algal flora and we are having only a small number of species, which are pollution tolerant. We are losing (rather lost) hundreds of species of algae before knowing them. In case of “charismatic wildlife” case at least we know that we are losing Tiger, Elephant and so on, but here we are losing without knowing what we are losing. This year 2 new species of diatoms was described from the lakes located in outskirts of Bangalore ( These 2 new species occur only in unpolluted lakes in Bangalore outskirts and not in the lakes inside city. We might lose them in future by polluting the lakes in Bangalore’s periphery!

    4. Diatoms (one of the major group of algae) are known to be excellent environmental indicators. I and my co-workers are in the process of describing some more new species from Bangalore and Tumkur districts. Further we are also developing diatom based pollution monitoring techniques for urban lakes based on our experience with Bangalore lakes.

  4. Karthick Bala says:

    5. From Gubbi Labs (a private research collective) we have developed a free online Environmental Education tool for school students to explain how our activities change the diatom composition in water bodies. Currently this program in available in English, Kannada, Marathi and Tamil (apart from many other international languages). We are in the process of expanding it to other major Indian languages. (One can play and learn here

    We are doing a free demonstration of this program in many schools across Bangalore and surrounding regions. If interested, we will be happy to give a demo too!

    6. So what is the solution to keep the algal flora diversive and alive (a) Stop the sewage inflow, even the “so called” restored 11 lakes are also receiving inflow of sewage. (b) Upgrade the sewage treatment facilities as soon as possible to meet the current requirement. By treating part of sewage we are continuing to pollute the lakes as well as consuming energy to run those treatment plants. (c) Bring in some policy level changes and awareness across the board to conserve the lakes and their catchment. Otherwise, we may stand to lose all that is remaining. Nevertheless, the trend is not encouraging in Bangalore.

  5. M V Bhaskar says:

    We have an unique solution to this problem.

    We cause a controlled bloom of Diatoms to keep out other algae.

    Our US distributor calls this Biological Acceleration.

    This process was in fact invented in Bangalore and demonstrated in Putenahalli lake in 2005 and again in 2011.

  6. Arathi Manay Yajaman says:

    Karthick and MV Bhaskar, thanks for the information.
    MV Bhaskar – you must be referring to Sarakki Lake. We have not used anything in our Puttenahalli Lake in JP Nagar 7th Phase (next to Brigade Milennium/ MLR CC)

  7. Arathi Manay Yajaman says:

    We’ve identified the “green” to be a water fern called Salvinia and not algae. We are looking for contractors/ fishermen/ any others to help in deweeding. Please contact 7259722996 if you know anyone who will undertake this job. Having a boat/ coracle should not be a constraint as it can be made available on site.

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