Background Biomarkers have become a valuable tool in environmental assessment, since they contribute to predicting contaminants in monitoring programmes. This study aimed to investigate the toxicity of heavy metal pollution in Lake Qarun using a multibiomarker approach (morphological, oxidative stress, genotoxicity, stress proteins) in Solea aegyptiaca fish. During the winter and summer seasons, water and fish samples were collected from different locations along Lake Qarun; western and northern sectors were away from any source of pollution, while southern and eastern sectors were exposed to effluents discharged from El-Wadi and El-Bats drains, respectively. The environmental quality, as well as the accumulation of metals (Fe, Cu, Zn, Cd, Pb, Ni) in fish gills, liver, and muscles were assessed. Data were integrated using the integrated biomarker response index (IBRv2) for biomarker response interpretation. Results Water quality and bioaccumulation of heavy metals revealed a highly significant difference between samples collected from polluted sectors and those collected far from drainage water, and, seasonal differences were detected. Growth indices revealed a significant difference between sites and seasons. Fish from the western sector had the highest total antioxidant capacity in their gills, liver, and muscles, with no seasonal differences detected. However, the maximum value of malondialdehyde, protein carbonyl, 8-hydroxy-2′deoxyguanosine, metallothionein, heat shock protein 70, and DNA strand breaks in gills, liver, and muscles was detected in the polluting sectors. It revealed a significant difference between seasons, with the highest value during the winter season. According to IBRv2 results, the most effective biomarkers in this study were malondialdehyde and 8-hydroxy-2′deoxyguanosine in gills, protein carbonyl and metallothionein in the liver, heat shock protein 70 in gills and liver, and DNA strand break in gills, liver, and muscles. Conclusions This multibiomarker approach contributes to distinguishing between locations with varying levels of anthropogenic pollution, identifying the drainage water-exposed sectors as the most stressed and the winter season as the most critical time for Solea aegyptiaca owing to spawning. The biomarkers chosen are effective indicators in Solea aegyptiaca under stress, indicating the potential for environmental monitoring. Graphical Abstract

Lake Qarun, located in El-Fayoum province, is one of the most important Egyptian water bodies. It is potentially at risk due to pollution and environmental degradation. This lake suffers from several environmental problems (Mohamed & Gad, 2008). Lake Qarun has witnessed several drastic changes affecting its role as economic potential site ARTICLE INFO