The impounding level of 175 m for the Three Gorges Reservoir (TGR) is of vital importance for efficient flood control, power generation and convenient navigation in China. However, little is lcnown about the spatial distribution and toxicological risks of major pollutants in the Three Gorges Reservoir Area (TGRA) at that stage. The aim of this study is to probe the ubiquitous polycyclic aromatic hydrocarbons (PAHs) contamination and toxicological impacts in the surface water of the TGRA at the highest water impoundment level of 175 m. Our results showed that the EPAHs levels ranged from 83 to 1631 ng/L in the upper reaches, 354 to 1159 ng/L in the middle reaches, and 23 to 747 ng/L in the lower reaches of the TGRA. Source apportionment of PAHs indicated that coal combustion, industrial emissions, heavy traffic, agriculture and shipping activities were the primary sources. Compositional pattern highlighted >85% dominancy of low molecular weight (LMW) PAHs in the reservoir. Risk assessment based on risk quotients (RQs) implied moderate to high ecological risks: the upper reaches> the middle reaches > the lower reaches. However, gene expression profiles portrayed contrary scenario because of the presence of relatively higher footprints of high molecular weight (HMW) PAHs in the middle and the lower reaches, which was confirmed by Cox hazard proportional model. Moreover, the transgenic zebrafish Tg(cyp 1 a:gfp) induced by PAHs also expressed stronger fluorescent signals in the middle and lower reaches. Taken together, different approaches were employed to firstly reveal the real status of ecological toxicity of PAHs and explore the underlying mechanisms at the highest impounding level of 175 m in the TGRA. (C) 2016 Elsevier B.V. All rights reserved.