Status of Wetlands in Bangalore

To characterise the wetlands in Bangalore, seven tanks were selected based on their location and the source of pollution-Bannergatta, Hebbal, Kamakshipalya, Madivala, Sankey, Ulsoor and Yediyur. Grab sampling was done at the inlet, centre and outlet in most of the waterbodies studied to assess their physical and chemical qualities at monthly intervals, except during some seasons when the centre of the waterbody was not accessible. Variability of physico-chemical parameters in these lakes is discussed in the following section.

  BANNERGATTA TANK

  The Bannergatta tank (Deepakanalla), situated in Bannerghatta National Park, is in the southern part of the city. Amidst thick forest, covering an area of about 2 hectares, it serves as a source of drinking water for the wild animals. The tank provides habitat for Indian crocodiles, many forms of fishes and variety of birds (egrets, kingfishers, etc). The tank with no major source of pollution and located close to the nature camp was chosen for water quality assessment, which was done for ten months at a point towards the outlet (boating is not done in the tank).

Water was clear with non-objectionable odour throughout the study period, with temperature ranging from 21-29ºC (26.1± 2.6ºC) and transparency of 30-50 cm showing the clarity of the water body. The low turbidity values further illustrate the clean status of the water-body.

pH: pH of the water-body is the measure of acidity or alkalinity in the aquatic system, which determines the various chemical and biological interactions occurring within. The water samples were found to be alkaline throughout the study period with pH ranging from 8.1 to 9.7, which could be attributed to the dissolved alkaline substances (Figure 7.1).

Electrical Conductivity: The electrical conductivity (EC) was in the range of 0.20±0.06 milli Siemens/cm indicating less dissolved solids and no major source of pollution (Figure 7.2).

Dissolved Oxygen (DO), Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD): The important parameters that determine the water quality of the lake are DO, BOD and COD. DO ranges from 6.0-7.8 mg/L showing the healthy status of the water body (Welsh, 1957). The BOD and COD values ranging from 2 ± 0.79 mg/L and 19.4±7.2 mg/L respectively, further supplement the non-pollution of the water-body (Figure 7.3).

Total solids (TS), Total dissolved solids (TDS) and Total suspended solids (TSS): The suspended solids ranged from 20-132 mg/L. The high values noticed during July-Sept 1997 might be due to rain. Similar trends were noticed with total solids, ranging from 78-242 mg/L. The total dissolved solids were found to be 93.8 ± 27.7 mg/L, well within the WHO, Aesthetic Quality Guidelines (that suggest 1000 mg/L as the limit). The low value of solids indicates that water is not polluted (Figure 7.4). 

Heavy metals: The various heavy metals that included copper, lead, iron, zinc, nickel, cadmium and chromium were found at non-detectable levels.

SANKEY TANK

During the latter half of the 19th Century, Col. Sankey constructed a tank in the Western part of the city, between Malleswaram and Sadashivanagar areas, to meet the drinking water demand. The tank has a well-maintained park and a corporation swimming pool at the southern part, and a nursery towards the north, adjacent to the tank. It also attracts large populations of migratory birds apart from small time fishing activities. The tank presently has no major source of pollution except for some washing activities towards the southern and western parts of the tank. The water is presently used for watering plants by the forest department. The tank serves the recreation requirement of the region and has a boat club run by the Karnataka State Tourism Development Corporation (KSTDC). The monthly water samples were collected at three points (inlet, centre and outlet) for twelve months, for evaluating the physico-chemical and biological parameters. The water was clear throughout the study period with non-objectionable odour. Temperature of the water body ranged from 21 to 30 °C.  The clarity of water is indicated by low turbidity values ranging from 6 to 14 NTU and high transparency of over 25 cm.

pH: The pH of the water samples during the study period was mostly neutral at all points ranging from 7.2-8.4. The standard pH range for unpolluted natural water bodies lies between 6.0-9.0 (Figure 8.1).

Solids: The water samples showed lower concentration of solids during the study period. Lower TDS values of 228±47.75, 234.18±30.97, 247.2±42.8 mg/L were found at inlet, centre and outlet respectively (Figure 8.2). The TS ranged from 260-446 mg/L towards inlet, 264-398 mg/L at centre and 276-408 mg/L at outlet (Figure 8.3).  Similarly low TSS values at all sample points indicate that the tank has less plankton density and pollution load.

Electrical Conductivity (EC): The electrical conductivity of water samples at centre and outlet was 0.49±0.05, and 0.55±0.29 mS/cm towards inlet. Lower value of EC suggests that the tank has no major source of pollution. The high value of EC noted during April 1997 at outlet was due to inflow from the nursery side (Figure 8.4).

Total Hardness (TH): The dissolved salts of carbonate and bicarbonates of divalent cations (such as calcium and magnesium) cause the hardness in water. Relatively higher value of about 150 mg/L of total hardness was found at inlet, which may be due to runoff from the nursery (Figure 8.5) (which uses hardness-inducing substances such as lime).

Dissolved Oxygen (DO):  The DO values of the lake are 6.6±0.9 mg/L, 6.7±0.9 mg/L and 6.6±1.0 mg/L at inlet, centre and outlet of the tank respectively. The DO at all sample points of the lake showed nearly similar values throughout the study period (Figure 8.6).

Biological Oxygen Demand (BOD):  Low BOD values ranging from 1.7-7.0 mg/L were noticed at all points in the lake, indicating low degree of pollution (Figure 8.7).

Chemical Oxygen Demand (COD): Low values of COD ranging from 15-105mg/L at inlet, 14-94mg/L and 12-112 mg/L at inlet, centre and outlet respectively clearly shows the water in this lake is relatively less polluted (Figure 8.8).

  Cations: The cations showed little variations with time during the study. Calcium varied from 31.0 - 118.0 mg/L at various points measured in the tank. Low values of potassium ranged from 2.0-11.0 mg/L and similar trends were noticed for all cations measured at all sampling points (Figure 8.9 – 8.11).

KAMAKSHIPALYA TANK

  The Kamakshipalya tank situated in the western part of the city covers a small area, less than a hectare. The tank is encroached on all the sides by slums. A number of small-scale industries located in the vicinity manufacture plastic products and undertake electroplating (chromium), etc. The tank once a source of drinking water (till the late 80's) receives direct effluents from both industries and the surrounding residential areas of Basaveshawaranagar, Saligrama, Kamakshipalya, etc. The water quality was monitored for a period of six months at two points towards the periphery of the tank (as no boating facility was available to carryout water sampling at the centre). Sampling points chosen were  (a) behind the slums and  (b) towards the outlet, where effluents from neighbouring dye industries enter the tank. Colour of the water was blackish, with high turbidity and obnoxious odour throughout the study period. Turbidity of the water body was high, ranging from 28 to 362 NTU (Nephelometric Turbidity Units). The tank due to its poor water quality has become a breeding ground for mosquitoes, and due to poor management, is a cesspool for pollutants, supporting negligible biodiversity.

pH: The pH of the lake during the study period was acidic,  ranging from 6.5‑7.5. This could be due to the decay and decomposition of the accumulated organic matter (Figure 9.1).

Electrical Conductivity (EC): The EC ranges from 1.27-2.09 milli Siemens/cm, indicating high amount of dissolved solids (Figure 9.2).

Total Dissolved Solids (TDS): Total dissolved solids of the water body were found to be 710.3 ±114.2 mg/L at the point behind the slum and 843.3 ±179.2 mg/L towards the outlet, indicating a high level of pollution (Figure 9.3).

Dissolved Oxygen (DO): DO ranged from 0.5 to 3.9 mg/L, due to the presence of high amounts of organic substances leading to biological activities such as respiration and decay processes within the system. This lower DO value reflects the septic condition of the lake (Figure 9.4).

Chemical Oxygen Demand (COD): COD value ranges from 170 to 621 mg/L. High values were observed during much of the study period (over 300mg/L), indicating severe chemical pollution due to sewage load. Rains during January 1997 lowered the COD value due to dilution. The permissible limit for inland surface water is 250 mg/L (Central Pollution Control Board - CPCB Standards) (Figure 9.5).

Biological Oxygen Demand (BOD): BOD is a very important parameter that estimates the amount of oxygen required for biodegrading organic substances present in the lake. BOD ranges from 27 to 192 mg/L, indicating oxygen demand for various biological activities (Figure 9.6). Higher BOD values noticed in samples collected behind slums are due to dumping of organic wastes.

Chlorides: The chloride value of samples was 166.4±76.898 mg/L at the point behind the slum and 221.7±67.1 mg/L at the outlet. These high values observed reflect pollution due to effluents of both domestic and industrial sectors (Figure 9.7)

Total Hardness: The samples showed high values of hardness ranging from 254 to 548 mg/L. The major source of hardness, detergents, get into the water body from the dye industries situated adjacent to the tank and from the residential colonies (Figure 9.8).

Ca, Mg, K, Na: Higher sodium concentration was found to be 149 ± 73.2 mg/L suggesting pollution by domestic sewage and high calcium ranging from 57.2 to 192.0 mg/L, which could be due to detergents washed into the water body (Figure 9.9). 

Higher values of cations were noticed towards the outlet. The high sodium concentration ranging from 93 to 260 mg/L suggests pollution by domestic sewage. The drop in the calcium concentration during January 1997 is due to dilutions because of rain during the season (Figure 9.10).

Total Suspended Solids: Higher values of suspended solids were noticed during the study period ranging from 108 to 410 mg/L (the tolerance limit for inland surface water is 100 mg/L) which is due to influx of sewage (Figure 6.11). High amount of suspended solids leads to depletion in DO (especially if it is organic) apart from imparting high turbidity (Figure 9.11).

Madivala tank is the second biggest in Bangalore, after Bellandur tank. The tank is situated in B.T.M. layout between Bannergatta and Hosur roads, covering an approximate area of about 115 hectares. This tank has a park and a boating club run by KSTDC for recreational purpose. It receives voluminous amounts of untreated sewage of both domestic (mainly) and industrial sectors from surrounding areas of Jayanagar, B.T.M. layout, Madivala and from other localities. The tank gets detergents from washing and other domestic effluents from a 'Dhobighat' (washing clothes at large scale by washer men) and an associated slum. The pollution status of the tank was evaluated by analysing the various physico-chemical and biological parameters at the inlet, centre and outlet of the tank. The tank was covered with water hyacinth for 4 months of the study period during which time sampling at the centre of the tank was not done. The color of the water was found green for much of the study period, mainly due to higher plankton density. During Sept-Oct 1997, water was clear due to dilution on account of rain. The water temperature was between 21ºC (during Dec 1996 – Jan 1997) to 29ºC (Apr-May 1997).

pH: The pH range for inland surface water is 6.0 - 9.0 (Welch, 1952). The pH of the water samples of Madivala tank ranged from 7.2 to 9.1 showing alkalinity, which is due to the using up of the available free carbon-di-oxide on account of plankton activity and sewage (Figure 10.1).

Electrical Conductivity:  EC varied from 0.7-1.3 mS/cm at the inlet and 0.63-1.4 mS/cm at the outlet, due to higher dissolved solids from the sewage (at inlet) and washing activities that bring in dissolved salts at outlet. The values at the centre ranged from 0.63-0.79 (Figure 10.2).

Total Dissolved Solids: The total solids averaged at 464.3 mg/L (S.D 71.5) at inlet, 396.9 (S.D 68.9) at outlet, and 321.4 (S.D 112) at centre of the lake. Higher values of TDS were noticed at both outlet and inlet during Apr-May 1997 due to decreased water level (Figure 10.3).

Dissolved Oxygen: The DO concentration throughout the study period did not vary much from one station to another, ranging from 1.8 to 8.0 mg/L, 2.3 to 8.2 mg/L and 2.6 to 8.3 mg/L at inlet, centre and outlet respectively. DO values of the lake showed to be a limiting factor for the lake’s health. Low DO values during Feb-Apr 1997 were due to water hyacinth (Figure 10.4).

Total Hardness: Total hardness of water samples were 206±34.4 mg/L at inlet, 181.7± 29.3 mg/L at centre and 199.3±29.4 mg/L at outlet during the study period. This high value of hardness is due to domestic sewage and washing activities that take place on the tank bed (Figure 10.5).

Biological Oxygen Demand:  The BOD values of water samples vary from 4.0 to 42.0 mg/L towards the outlet and inlet. The higher values noticed during May-Jul 1997 were due to water hyacinth blooms, sewage and precipitation runoff (Figure 10.6).

Chemical Oxygen Demand: Organic and inorganic chemical pollution in water samples are reflected by high values of COD. The values in Madivala lake ranged from 46.2 to 282.0 mg/L. Higher values of COD noticed during May-July 1997 could be due to sewage and surface runoff towards the inlet and detergents from washing by washer-men at the outlet (Figure 10.7).

Chlorides: The high chloride contents of 134.8 mg/L noticed at the inlet is an evidence of organic pollution from domestic pollutants (Kataria, H.C., et al 1996) and 127.8 mg/L at the outlet, which is mainly due to detergents (Figure 10.8).

Cations:  The calcium content of the water sample indicated a decrease from 50.5 to 33.6 mg/L during Nov 1996-Jan 1997 and increased during Feb-Apr 1997. Potassium and magnesium are 22.5±6.0 mg/L and 26.1±7.4 mg/L respectively. The fluctuations in sodium values can be attributed to sewage (Figure 10.9).

Similar trends in the Ca, Mg, K, and Na values were noticed towards the outlet of the tank (Figure 7.10).

The Yediyur tank situated on the Kanakapura road in Jayanagar area of the city covers an area of about a hectare. The tank has a park and residential layout in its vicinity. It receives both industrial and domestic sewage apart from solid wastes dumped across the periphery of the tank. It is heavily infested with plankton, mainly microcystis, indicating pollution. The tank serves as a breeding ground for mosquitoes and acts as a cesspool leading to obnoxious odour. It has two major inlets and two outlets. In order to assess the level of pollution and to suggest restoration measures, water quality of the tank was monitored for a period of about twelve months at two points, one towards the centre of the tank and the other towards the major inlet point.

The tank water was greenish owing to high plankton density. High turbidity noticed is due to plankton and sewage. Transparency of 5-14 cm indicates low light penetration. The temperature of the water measured during sampling time (10-11 am) varied from 23-29ºC.

pH: The pH is affected not only by the reaction of carbon-di-oxide but also by the presence of organic and inorganic solutes in the water. The pH at both the sample points was mostly towards alkalinity ranging from 7.5 to 10.1. The decrease in pH during the monsoons may be due to decreased photosynthetic activity and the inflow of storm water. Maximum values in summer may be due to increased photosynthetic activity by algal blooms. The alkaline pH could also be due to untreated domestic sewage getting into the water body (Figure11.1).

Dissolved Oxygen: Dissolved oxygen is important for all living organisms. The main source of dissolved oxygen in aquatic system is either direct diffusion from air or from photosynthetic activity of the autotrophs. It is an important parameter indicating the health status of the water body. DO ranged from 4.0 to 10.0 mg/L at the centre and 3.8 to 8.9 mg/L towards the inlet. Relatively lower values at the inlet were due to sewage and solid waste preventing air-water interaction and decomposition of organic matter leading to decreased/low dissolved oxygen. The higher values noticed at the centre may be due to higher planktonic density resulting in higher photosynthetic activity (Figure 11.2).

Chemical Oxygen Demand: COD is an important measure of pollution in an aquatic ecosystem to estimate the carbonaceous factor of the organic matter. The COD values ranged from 84 mg/L in Oct 1997 to a high of 378 mg/L during Apr 1997 at the centre and 112 mg/L in Sept 1997 to a high of 370 mg/L during Apr 1997 towards the inlet. During April 1997, high values of COD were noticed, which may be due to less volume of water (after evaporation) and continued inflow of sewage. The lower values during Sept-Oct 1997 were due to inflow of catchment runoff resulting in dilution (Monsoon) (Figure 11.3).

Chlorides: High concentration of chlorides is an indicator of pollution due to high organic wastes of animal or industrial origin. In the present study, high values of chlorides were noted at an average of 109.8 mg/L at  centre and 96.0 mg/L towards the inlet (Figure 11.6).

Total Hardness: The main cause of hardness in natural water is due to calcium and magnesium salts combined with carbonates and bicarbonates. The value of total hardness ranges from 157.1± 30.5 at centre to 146.5 ± 34.1 mg/L at inlet. The main source of hardness is domestic and industrial washing flowing into the lake (Figure 11.7).

Total Dissolved Solids: The Total Dissolved Solids (TDS) include anions and cations in dissolved form. High TDS indicates pollution. The study showed that dissolved solids were higher towards the inlet ranging from 208-428 mg/L at an average of 272.0 mg/L, which is attributed to the inflow of sewage. Similarly, the TDS ranges from 212 to 402 mg/L at an average of 296.4 mg/L in the centre, due to transport of pollutants from the inlets. Dissolved solids were noticed to be more during summer at both points, which may be due to lowered water level (Figure 11.8).

Cations: The major cations calcium, magnesium, potassium and sodium showed noticeable variation. Calcium, magnesium and sodium are 74.2±19.5, 20.2±10.9 and 80.1± 12.6 mg/L respectively, and the higher range can be attributed to pollution from domestic and industrial sources (such as detergents, food wastes, etc) (Figure 11.9 – 11.10).

Similar results of the higher values of cations obtained at inlet, indicate pollution by domestic and industrial sewage.

Hebbal tank is situated in the northern part of the city covering an area of about 75 hectares, one of the biggest tanks in Bangalore.  It supports agriculture and small-scale fishing and serves as a water source for the forest nursery nearby. The tank receives untreated domestic sewage from B.E.L layout, Vidyaranyapura, Hebbal and surrounding areas apart from vehicular pollution due to heavy traffic on the adjoining highway (NH-7). It is infested with water hyacinth for much of the year. The tank is ecologically important as it supports a large population of migratory birds, which includes egrets, cranes, coots, kingfishers, etc. Once a major drinking water source to the surrounding areas, it is on the verge of death due to pollution. Samples collected at the inlet, centre and outlet (sampling at centre was done based on the availability of a boat and absence of water hyacinth) were analysed for physico-chemical and biological characteristics on a monthly basis.

The colour of the water body was dark grey towards the inlet (due to sewage), greenish towards centre and outlet (as a result of plankton). Higher values of turbidity were noticed at the centre and inlet due to plankton and sewage. Transparency ranges from 9.0-21.5 cm at various points in the tank indicating low light penetration. Temperature of the water during sampling time (10-12 am) was in the range of 20-30ºC.

pH: pH is a dynamic parameter in an aquatic ecosystem varying with changes in physical and chemical properties over a period. pH of the tank was found mostly in the alkaline range from 7.5 to 8.9 at sample points of the lake. The high pH noticed could be attributed to characteristics of the incoming sewage and plankton activity. Plankton activities increase pH by making use of the available carbon-di-oxide (Figure 12.1).

Electrical Conductivity: The electrical conductivity noticed during the study period was high, varying from 1.2 to 1.5 mS/cm. Higher EC values were noticed during Apr-Jul 1997, which could be due to high dissolved solids from sewage and reduced volume of water due to evaporation. The decreased EC during Sept-Oct 1997 could be attributed to dilution on account of runoff due to rains (Figure 12.2).

Total Solids: The main source of total solids to Hebbal tank is inflow of sewage and surface runoff. TS showed higher values at centre during Nov 1996 – Feb 1997 (737.5 ±22.9 mg/L) compared to average values of outlet and inlet, which is due to high plankton density. TS were found to range from 600-968 mg/L at inlet, 702-766 mg/L at centre and 556-902 mg/L at outlet. A high value at inlet was mainly due to sewage and agricultural run-off (Figure 12.3).

Total Dissolved Solids: The dissolved solids showed higher values of 514.5±172.1 mg/L, 548±199.7 mg/L, and 485.6±143.6 mg/L at inlet, centre and outlet respectively. The steep fall in the values of TDS during Aug 1997 was due to increased water levels from rain and may be due to sampling done towards the periphery of the tank (owing to non-availability of a boat) (Figure 12.4).

Dissolved Oxygen: Throughout the study period, low values of dissolved oxygen were noticed at the inlet (2.6-7.1 mg/L) compared to the outlet (2.5-7.3 mg/L). Low dissolved oxygen at the inlet is due to sewage getting into the tank. The higher DO during July 1997 at both points was due to sampling time (done at noon, when photosynthetic activity by the phytoplankton is maximum, releasing oxygen) (Figure 12.5).

Biological Oxygen Demand: The BOD observed at inlet, centre and outlet was 22.5±5.8 mg/L, 20.0±4.8 mg/L and 20.6±5.2 mg/L respectively. The BOD at the inlet was understandably high (11.0-32.0 mg/L) due to sewage entering the tank there (Figure 12.6).

Chemical Oxygen Demand: The COD values of the tank range from a low value of 56.0 mg/L during Oct 1997 due to rains, to a high of 386.0 mg/L during Mar 1997 at inlet, 58.3 to a high of 348 mg/L at centre and 41.0 to 362.0 mg/L towards the outlet. The higher values noticed during Feb-Mar 1997 could be due to sewage entering during the sampling time and increased chemical concentration due to reduced volume of water during summer (Figure 12.7).

Cations: The various cations analysed showed higher values at all the points within the tank (Figure 12.8 – 12.10).

Calcium: The values of calcium ranges from 68.9 to 248.0 mg/L at inlet, 73.2 to 160.0 mg/L at centre and 60.6 to 244.0 mg/L at outlet. The high values could be attributed to domestic sewage, which has detergents in it.

Sodium:  The high values of sodium ranging from 92 to 176 mg/L were observed at different points in the lake. High values could be due to domestic sewage getting into the tank. Nitrates, phosphates and potassium analysed to evaluate the eutrophic condition of the lake ranged from ND to 4.0.

  ULSOOR TANK

Ulsoor tank, situated in the eastern part of the city, is spread over an area of about 50 hectares. It has three islands and receives direct industrial and domestic effluents from the surrounding areas of Tannery road, Ulsoor, etc. It has a park in its vicinity, a corporation swimming pool adjacent to the tank and a boat club run by KSTDC (Karnataka State Tourism Development Corporation) for recreational purpose. Madras Engineering Group (MEG) uses the tank for boat training. The colour of the water is greenish, with objectionable (fishy) odour. The temperature of the lake during sampling periods ranged from 22-31°C with low transparency (4.5-16 cm) and high turbidity (68-290 NTU).

pH: The pH of the monthly water samples was found mostly towards alkalinity ranging from 7.5-11.0. The high pH observed might be due to high plankton activity (which makes use of the available carbon-di-oxide) and sewage (Figure 13.1).

Electrical Conductivity: EC values ranged from 0.6-1.2 mS/cm. The high values of EC were due to high dissolved solids (Figure 13.2). High EC would affect plant life of the surrounding ecosystems and the aquatic biological food chain and ecology adversely (Ramakrishna Parma et al, 1990).

Solids: Total solids ranged between 460-884 mg/L and suspended solids were about 200 mg/L at all sampling points in the lake during the study period. The high values of suspended and dissolved solids (246-644 mg/L) are a result of high plankton density (Figure 13.3-13.5).

Dissolved Oxygen: DO content was found to be 6.9±1.2 mg/L at inlet, 9.1±1.0 mg/L at centre and 9.0±1.2 mg/L at outlet. High dissolved oxygen content of Ulsoor tank indicates high plankton activity at the time of sampling (10-12 am) (Figure 13.6

Biological Oxygen Demand: The BOD values of the tank ranged from 10.0 to 31.0 mg/L with higher values (avg. 22.6 mg/L) at inlet, which receives influx of sewage. The permissible limits for BOD for irrigation water are 150 mg/L (Figure 13.7)

Chemical Oxygen Demand: The COD values were found to be 231.4 mg/L, 216 mg/L and 221.3 mg/L at inlet, centre and outlet respectively. The high values of COD are a result of pollution from both industrial and domestic sectors (Figure 13.8).

Chloride: The study showed high concentrations of chlorides at 131.4 mg/L at inlet, 108.0 mg/L at centre and 113.0 mg/L at outlet. High concentration of chlorides is considered to be an indicator of pollution due to high organic wastes of animal and industrial origin (Figure 13.9).

Total Hardness: Hardness of the water samples ranged from 126-196 (avg. 159.5) mg/L at inlet, 114-200 (avg.157.5) mg/L at centre and 118-202 (158.7) mg/L towards the outlet. The high values could be mainly attributed to the inflow of sewage (Figure 13.10).

Cations: The various cations analysed (Ca, Mg, K, Na) showed higher values at all points in the lake. Calcium showed values of 86.9±32.9 mg/L, 89.5±33.5 mg/L and 86.1±40.7 mg/L at inlet, centre and outlet respectively, which is due to detergent pollution (Figure 13.11- 13.12). High values of sodium ranging from 66-160 mg/L, shows pollution due to domestic sewage.  

The results obtained from the twelve-month sampling of the seven tanks in and around Bangalore city revealed that most of them were polluted due to the inflow of domestic sewage and industrial effluents. Bannergatta tank was relatively clean due to its location (inside the national park) and similarly Sankey was unpolluted as the water was mainly used for boating and watering the forest nursery. In contrast Madivala, Ulsoor, Yediyur, Kamakshipalaya and Hebbal were polluted as to render the water unusable for any purpose. Kamakshipalaya was eutrophic as elucidated by the DO (0.5 to 3.9 mg/L), BOD (27 to 192 mg/L) and COD (170 to 621 mg/L) values. Madivala, the second largest lake of Bangalore city was polluted due to the inflow of domestic wastes and detergent from the nearby residential areas and was covered by water hyacinth for most of the study period. The organic and inorganic chemical pollution in water samples are reflected by high values of COD (84 – 374 mg/L) and total hardness (181 – 206 mg/L). Yediyur tank covering about a hectare receiving both domestic and industrial effluents  showed high COD (84 – 378 mg/L) values and was infested with microcystis (an indicator of pollution). Hebbal tank one of the largest tanks although supporting agriculture was highly polluted due to the inflow of untreated domestic sewage and vehicular pollutants from the adjacent national highway. High values of  TSS (568 – 968 mg/L) and COD (41 – 368 mg/L) revealed an urgent need to restore the lake as it supports  a large number of migratory birds. Hebbal and Madivala tanks are being restored under Indo-Norwegian Environment programme (Co-ordinated by the Karnataka State Council for Science and Technology). Ulsoor tank situated in the heart of the city receives domestic effluents and industrial wastes. Almost all the parameters were in excess of the standards prescribed for surface waters (CPCB, NEERI and WHO).  The poor state of waterbodies evident from water monitoring results stress the need for implementation of restoration and conservation strategies. This requires thorough appraisal of wetlands values.