Environmental sustainability of the Chitgar Lake construction project in Tehran, Iran, was evaluated by a life cycle assessment (LCA) method in two phases of construction and operation using SimaPro 8.2.3 software. The results of analysis by Centre voor Milieukunde Leiden (CML) and IMPACT methods demonstrated that during the construction and operation (assuming 80 years of operation) phases of the lake 0.102 and 0.141 Mt of CO2eq (affects global warming), 0.015 and 0.021 Mt of 1,4‐dichlorobenzene (DB)eq (results in toxicity for humans), 657.155 and 807.425 tons of SO2eq (leads to acidification), 150.123 and 69.374 tons of eq (causes eutrophication), 1597 and 2265 terajoules of primary energy (damages the resources), 0.1 and 0.138 Mt of CO2eq (impacts on climate change), 18205330.45 and 11424387.32 potentially disappeared function (PDF) × m2 × yr (harms the quality of the ecosystem), and 165.37 and 104.94 disability‐adjusted life year (DALY) (threats the human health) are caused, respectively. Electricity consumption has the greatest environmental impact on the operation phase of the lake. Furthermore, the operation phase of the lake is more harmful to the environment and human health compared to the construction phase.