Physico-chemical parameters of lake: Table 1 lists physic-chemical parameters of  water samples collected from Chikkabettahalli lake. Parameters that were analysed are:

Temperature: It is an important factor for aquatic life as it regulates the maximum dissolved oxygen concentration of the water, controls the rate of metabolic activities, reproductive activities and therefore, life cycles. The temperature of Chikkabettahalli lake ranges between 23.40C (S1) to 22.80C (S2).

Dissolved Oxygen: Dissolved oxygen (DO) helps in aquatic respiration as well as detoxification of complex organic and inorganic matters (through oxidation). The presence of organic wastes imposes a very high oxygen demand on the receiving water, leading to oxygen depletion with severe impacts on the water ecosystem. The effluents also constitute heavy metals, organic toxins, oils, volatile organics, nutrients and solids. DO of the analysed water samples varied between 2.44 to 2.85 ppm. The lower DO values are indicative of fast oxidising chemicals in the immediate vicinity. The DO was very low which indicates water pollution. The macrophyte cover is also responsible for low DO values.

Total Dissolved Solids (TDS): TDS in water impacts the domestic water usage for cleaning, bathing etc as well as drinking purposes. Total dissolved solids originate from organic sources such as leaves, silt, plankton, industrial waste and sewage. Other sources come from runoff from urban areas, road salts used on street, fertilizers and pesticides used on lawns and farms (APHA, 1998). Surface as well as groundwater with high dissolved solids are of inferior flavor and induce an unfavorable physiological reaction to the dependent population. TDS values in the collected water samples, ranged from 518 to 875 ppm across the lake. It was higher in S1 (closer to the inflow) and reduced in S2 of the lake. The TDS was higher in the S1 than S2 due to macrophyte and plankton cover.
pH: pH is a numerical expression that indicates the degree to which water is acidic or alkaline, with the lower pH value tends to make water corrosive and higher pH provides taste complaint and negative impact on skin and eyes. The pH value ranged from 7 to 7.36.
Chlorides:Chlorides are essentially potential anionic radical that imparts chlorosity to the waters. An excess of chlorides leads to the formation of potentially carcinogenic and chloro-organic compounds like chloroform, etc. Chloride values in samples ranged from 195-294 ppm. The value of chlorides was high in S1.
Sodium:Sodium (Na) is one of the essential cations that stimulate various physiological processes and functioning of nervous system, excretory system and membrane transport in animals and humans. Increase of sodium ions has a negative impact on blood circulation, nervous coordination, hence affecting the hygiene and health of the nearby localities. In this study, the concentration of sodium ranged from 197 to 494 ppm. The Sodium value was high in S1.
Potassium:Potassium (K) is an essential element for both plant and animal nutrition, and occurs in ground waters as a result of mineral dissolution, decomposing of plant materials and also from agricultural runoff. Potassium ions in the plant root systems helps in the cation exchange capacity to transfer essential cations like Ca and Mg from the soil systems into the vascular systems in the plants in replacement with the potassium ions (APHA, 1998). Incidence of higher potassium levels in soil system affects the solute transfer (active and passive) through the vascular conducting elements to the different parts of the plants. The potassium content in the water samples ranges between 43-137 ppm. The potassium value was higher in S1 due to decomposition of plant materials.
Alkalinity: Alkalinity is a measure of the buffering capacity of water contributed by the dynamic equilibrium between carbonic acid, bicarbonates and carbonates in water. Sometimes, excess of hydroxyl ions, phosphate and organic acids in water causes alkalinity. High alkalinity imparts bitter taste. The acceptable limit of alkalinity is 200 ppm. The alkalinity of the samples was in range of 272-321 ppm.
Total hardness: Hardness is the measure of dissolved minerals that decides the utility of water for domestic purposes. Hardness is mainly due to the presence of carbonates and bicarbonates. It is also caused by a variety of dissolved polyvalent metallic ions, predominantly calcium and magnesium cation although, other cations like barium, iron, manganese, strontium and zinc also contribute to Hardness. In the present study, the total hardness ranged between 308 to 556 ppm. It was higher in S1. High values of hardness are probably due to the regular addition of sewage and detergents.
Calcium: Calcium (Ca) is one amongst the major macro- nutrients which are needed for the growth, development and reproduction, in case of both plants and animals. The presence of Ca in water is mainly due to its passage through deposits of limestone, dolomite, gypsum and other gypsiferous materials (APHA, 1998). These contribute to the total hardness of the water. Ca concentration in all samples analysed periodically ranged between 92-183 ppm.
Magnesium: Magnesium (Mg) in one of the most essential macro-nutrients that helps as a co-factor in the enzyme systems and in the central metal ions that constitutes the chlorophyll molecule essential for plant photosynthesis. According to WHO guidelines, the maximum admissible limit is 50 ppm. In this study, the concentration of Magnesium ranged from 52-90 ppm.
Nutrients (nitrates and phosphates): Nutrients essentially comprise of various forms of N and P, which readily dissolve in solutions that are assimilated by microbes and plant root systems in the form of inorganic mineral ions. Accumulation of N as nitrates and P as inorganic P in aquatic ecosystems causes significant water quality problems leading to higher net productivity. Together with phosphorus, nitrates in excess amounts in streams and other surface waters can accelerate aquatic plant growth causing rapid oxygen depletion or eutrophication in the water. Nitrates at high concentrations (10 mg/l or higher) in surface and groundwater used for human consumption are particularly toxic to young children affecting the oxygen carrying capacity of blood cells (RBC) causing cyanosis (methemoglobinemia). In the present study, nitrate values ranged from 0.5 to 0.77 ppm and phosphate values ranged between 0.5 to 0.53 ppm.
Chemical oxygen demand (COD): COD is important parameter that indicates contamination with organic wastes. Chemical oxygen demand (COD) determines the oxygen required for chemical oxidation of most organic matter and oxidizable inorganic substances with the help of strong chemical oxidant. COD test is helpful in indicating toxic conditions and the presence of biologically resistant organic substances. In this study the COD values ranged from 24-28 mg/l.
Macrophyte diversity in the lake: Macrophytes, the aquatic macroscopic plants confine themselves to the shallow euphotic zone of the water bodies. In the littoral zone, macrophytes are the exploiters of plant nutrients from the sediments, which otherwise, are lost temporarily from the water. They assimilate nutrients directly into their tissues. The nutrients so logged in the body material are released only after death, decay and subsequent mineralization, thus, they play a role in nutrient dynamics and primary productivity of shallow systems. Therefore, seasonal growth rate patterns and population dynamics of macrophytes are very important. When there is enough room for colonization and abundant availability of nutrients, macrophytes show a high growth rate. Profuse growth and spread of macrophytes was noticed in this lake due to the availability of nutrients with the sustained inflow of untreated sewage. There were mainly 9 species found in the lake. Alternanthera philoxeroides, Alternanthera sessilis, Ludwigia perennis, Typha angustata, Cyperus sp, Solanum sp, Lemna gibba, Eichhornia crassipes, Spirodela polyrhiza were the main macrophyte species found in the lake. Alternanthera philoxeroides, Alternanthera sessilis and Solanum sp were the dominant macrophytes present in the lake (figure 4).
Algae as pollution indicators: Algae, the primary producers present in aquatic ecosystems forms an important component of biological assessment for evaluating water quality. Algae are indicators of different ecosystem conditions because they respond quickly to a wide range of physico-chemical as well as biological conditions, which will be evident both in their species composition and densities.
Table 2 lists macrophyte species of  Chikkabettahalli Lake. Common pollution-tolerant genera (Figure 5) that are present in the lake are Euglena sp. (Mahapatra et al., 2013a; Jafari et al., 2006), Lepocinclis sp. (Mahapatra et al., 2013a), Nitzschia sp. (Karthick et al., 2009; Jafari et al., 2006; Venkatachalapathy et al., 2013), Oscillatoria sp. (Jafari et al., 2006; Singh et al., 2011), Pandorina sp.,and Phacus sp., Cyclotella sp., Fragilaria sp. (Singh et al., 2011; Venkatachalapathy et al., 2013), Gomphonema sp. (Karthick et al., 2009; Venkatachalapathy et al., 2013), Navicula sp. (Hosmani, 2012; Singh et al., 2011), Pinnularia sp. (Hosmani, 2012) and Trachelomonas sp. (Solorzano et al., 2011).

Figure 4: Macrophytes of the lake 

Table 2: Algal species found in Lake

Figure 5: Microscopic images of algae in 40X

Euglenoids grow profusely under anoxic conditions in sewage fed lakes  with high organic loads (Mahapatra et al., 2013b). Nitzschia palea is typically found in phosphate enriched or organically polluted waters. Taxa that are moderately tolerant to phosphorus enrichment, includes Gomphonema sp. and Navicula sp. (Bellinger et al., 2006; Karthick et al., 2009). Cyclotella meneghiniana is resistant to extreme pollution present in eutrophic and electrolyte rich water bodies (Karthick et al., 2009).