Algae are thaloid organisms comprising of simple photosynthetic organism having unicellular to multicellular organization. Being lower organism, little attention has been paid to document algal resources across the lakes in particular and country in general. The present study was aimed to collect, identify and ecology of the algal flora of Kalar Kahar Lake and its Tributaries. A total of 341 species distributed across 89 genera, 53 families, 29 order, 11 classes and 7 phyla were identified from the study area. Highest number of families were contributed by phylum Bacillariophyta (24), followed by phylum Chlorophyta (13 families), Cyanophyta (11 families). Overall, 32 new taxa were recorded from the study area, out of which, 29 belonged to Bacillariophyta, 02 Cyanophyta and one Chlorophyta. Species richness (SR) was highest in the Lake in July during both the years, followed by August. While in the Tributaries, maximum SR was recorded in August and July during 2010 and 2011 respectively. Overall, 2011 was rich in algal diversity in both the Lake and the Tributaries. Similarly, cell density (D) was higher in 2011 than 2010. Bacillariophyta and Cyanophyta were constantly present in all months in the Lake and the Tributaries. Chlorophyta was present in all months except November in the Lake while in the Tributaries it was absent in January, February and November. Charophyta was present in October, November 2010 and May to July and October during 2011. 12 The highest number of species (α-diversity) was recorded during 2011 from both the Lake and the Tributaries (193 and 175 respectively), followed by the Tributaries (161 spp.) and the Lake (159 spp.) in 2010. There was opposite trend in the case of beta diversity (β) in which highest value was recorded during 2010. Maximum β-diversity was recorded from the Lake (2.14), followed by the Tributaries (2.12). Highest species were shared by Lake 2010-Lake 2011 pair (122 species), followed by Tributaries 2010-Tributaries 2011 (106 species), Tributaries 2010- Lake 2010 (83) and Tributaries 2011- Lake 2011(67 species). Amongst habitat pairs, Lake 2010-Lake 2011 possessed highest similarity Index (0.69) with least β-diversity followed by Tributaries 2010-Tributaries 2011 (0.63), Tributaries 2010-Lake 2010 (0.52) and Tributaries 2011- Lake 2011 (0.36). The Shannon–Weaver index in the Lake and the Tributaries varied from 2.14 to 3.42 and from 2.47 to 3.49 respectively suggesting that the water quality is moderately polluted to clean. Based on Importance Value Index (IVI), Microcystis–Nitzschia-Cyclotella formed algal community in the Lake during 2010, while Microcystis-Cladophora- Chara in 2011. In the Tributaries, Chara-Nitzschia-Microcystis and Microcystis- Phormidium-Nitzschia constructed dominant communities during 2010 and 2011 respectively. Water quality parameters viz., temperature, pH, dissolved oxygen, total dissolved solids , conductivity, total hardness, nitrates, phosphate, sulphate, light transparency, turbidity, iron, copper, zinc, lead and nickel varied significantly (P3 <0.05) amongst all the months during 2010 and 2011. Environmental variables such as dissolved oxygen, turbidity, phosphate, nitrate and total hardness significantly affected cell density (P <0.05) in the Lake, while water temperature, turbidity, phosphate and lead significantly (P <0.05) affected density in the Tributaries. The relationship of algal species with environmental data set was determined by Canonical Correspondence Analysis (CCA) using CANOCO software (version 4.2). Overall, environmental data sets such as nitrate, turbidity, copper, transparency, dissolved oxygen (DO) and zinc were found positively correlated in the distribution of specific taxa, while total hardness, water temperature, conductivity, total dissolved solids (TDS), and pH were negatively correlated for distribution of various taxa in the Lake during 2010-2011. In the Tributaries, environmental variables such as phosphate, total hardness, zinc, nickel, transparency, chlorophyll a, sulphate, lead, conductivity, TDS, copper and pH had positive relationship with algal composition during both years. DO in 2010 while nitrate and iron during 2011 exhibited negative correlation for algal distribution.