A group of Indian scientists including botanists, entomologists, ornithologists, mammalogists, herpetologists, aquatic fauna specialists, hydrologists, geographers, and social scientists, many with research experience in northeastern India, including the Dibang Valley in Arunachal Pradesh, have conducted a peer-review of the Technical Report prepared by the Wildlife Institute of India’s (WII) titled ‘Wildlife Conservation Plan for the impact zone of Etalin HEP, Dibang Valley District, Arunachal Pradesh’ (the ‘Report’). The Report was prepared in response to the Forest Advisory Committee’s (FAC) recommendation to conduct “a multiple seasonal replicate study on biodiversity assessment” of the 3097 MW Etalin Hydro Electric Project (HEP) in Dibang Valley, Arunachal Pradesh. The review has found that the study was conducted in under five five months from February to June 2018 and cannot be considered as a ‘multiple seasonal replicate’ study as it does not represent three seasons in Arunachal Pradesh. This survey period excludes seasonal migrants and/or crucial breeding times for certain species. Further, fieldwork was conducted in a very small area (‘Zone of Influence’, ZoI) compared with the area that will be directly and indirectly affected by the impacts of the HEP, with uneven sampling within the limited ZoI. While several groups of taxa were not surveyed, the Report outlines poor detectability for better studied taxa such as birds, without statistically accounting for low detections. Approaches and methods used to analyse field data, and produce results are inadequate, not clearly explained and, often, not scientifically recognised. Commonly-used methods (e.g., species accumulation curves) to analyse and report data on species richness and diversity were not applied to most taxa (except fish). Because of methodological and analytical deficiencies and exclusion of highly diverse taxa such as insects and other arthropods, comparisons with published research from Dibang Valley shows that the Report under-reports hundreds of species of butterflies and other insect groups and birds, and tens of species of orchids, mammals, and herpetofauna. The Report’s species checklists contain repetitions, improper taxonomic classifications, and incorrect distributions, including 12 butterfly species not known to occur in northeastern India and a bat species found only in Africa. Despite short surveys conducted using biased sampling methods, the Report provides direct evidence of 230 bird, 159 butterfly, 112 spider, 51 moth, 31 reptile, 14 amphibian, and 21 mammal species. Amongst these are several endemic (e.g., seven species of birds), range-restricted (e.g., six bird and three butterfly species), and threatened (e.g., eight mammal species) species, many of which are included in Schedule I of the Wild Life (Protection) Act, 1972. However, the Report ignores its own findings to outline mitigatory measures for some taxa while observing that “it was not possible to suggest any threatened species and habitat specific conservation plan” for others (e.g., mammals). Firstly, it is not clear how the FAC’s singular mandate of conducting a study on ‘biodiversity assessment’ was converted into a Wildlife Conservation Plan. Secondly, the few mitigatory measures recommended for some specific faunal groups in the form of butterfly, reptile parks, and nest boxes cannot be considered as well-designed ecologically meaningful measures. There appears to be an underplay of the negative impacts of the HEP throughout the Report. The section that relates to assessing socio-cultural impacts of the HEP suggests mitigation measures that lack a nuanced understanding of socio-cultural dynamics and interdependencies between people and the natural environment. Overall, the Report assumes the project as fait accompli implying that the Report’s findings have no bearing on the FAC’s decision to approve the project, ultimately making this exercise appear futile. Crucially, studies that inform high-level decision-making on historically significant projects, such as the Etalin HEP (which would be one the largest hydropower projects in the country), must go through a transparent and scientifically recognised peer-reviewed process given the pitfalls, numerous discrepancies, and gaps highlighted in this review. Such decisions have irreversible impacts on lives, livelihoods, and the environment.