Idku Lake is one of the northern coastal lakes in Egypt which receives huge amounts of wastewater from two main drains. This study was carried out to assess some water quality parameters of Idku Lake, using fish liver condition as a biomarker of water quality. Eleven parameters were measured in 10 stations of Idku Lake and evaluated by spatial distribution map using GIS analysis, in addition to the Eutrophication Index (E.I.). Investigated parameters unlikely distributed throughout the different regions of the lake with most parameters exhibited the highest levels near drains discharge regions and the minimum near El Boughaz. Adversely, phosphate reached the maximum level at El Boughaz. Salinity, electric conductivity and TDS drew nearly the same pattern of distribution which hit the maximum at the W and S parts and gradually decreased toward the N and E parts. Ammonia was recorded at a very low concentration while nitrate was at a high concentration compared to previous investigations. Consequently, the lake was recorded to be dystrophic in terms of the abundance state. Anthropogenic activity is the primary factor enhancing the inputs of nitrogen, phosphorus and other compounds to lakes, causing widespread eutrophication which affects aquatic food webs and ecosystem sustainability. A histopathological study was conducted on fish species (O. niloticus, O. aureus T. zillii,  Clarias gariepinus and Dicentrarchus labrax) collected from Idku Lake.  The most observed alterations were mononuclear cell infiltration, vacuolated hepatocytes, dilated central vein, compressed blood sinusoids, cytoplasmic vacuolations, hepatocytes necrosis, blood vessel congestion, patchy degeneration and low accumulation of mucopolysaccharide that indicates the remarkable toxic effect of Idku Lake water environment.