Water quality of Lake Tana is currently influenced by environmental pollution and anthropogenic activities. This study was aimed to evaluate the current spatiotemporal distribution of water quality in Lake Tana. Statistical analysis of 10 physicochemical parameters were done during four study seasons starting from July - 2018 to June – 2019. Analysis of variance (ANOVA) was conducted to measure spatiotemporal significant variation of physicochemical water quality parameters. Spatial maps were also generated using GIS tool (interpolation) to understand the spatial distribution of each water quality indicators in Lake Tana. Water Quality Index (WQI) was modeled in order to evaluate the general status about the lake water quality for aquatic and drinking desires. The ANOVA results indicated that, the physico – chemical water quality indicators have significant variation with time and place. As a result of Water Quality Index (WQI), 62% of the lake was laid on poor status for aquatic life requirements and its’ 59% was highly polluted for domestic consumptions. Currently, Lake Tana has low water quality problem associated with electric conductivity (EC), pH, total dissolved solids (TDS), ammonia (NH4) and nitrate( 𝑁𝑂3 −) as their analyzed values was agreed both spatially and temporally with international water quality standards of (EPA, 2018) and (WHO, 2017). However, Lake Tana was highly affected by turbidity and found with low dissolved oxygen (DO) both spatially and seasonally, as most of the measured values were beyond the standard limits. Generally, this paper revealed that the status of Lake Tana water quality was not convenient for human consumption uses without treatment works but with great cares and some restoration works the lake water is good for aquatic life.