A mega port is a vital ingredient of the country’s economy and its citizens. Despite its significant contribution, it creates numerous environmental impacts, especially during its construction. To achieve sustainable development, environmental mitigation measures stated in the environmental and health assessment report need to be strictly abided by. Since a mega port is constructed once in many decades, a case study (like this article), that presents how to minimize the marine environmental impacts, is very rare. We present how Thailand protects its surrounding marine environment during the construction of its biggest container port expansion (Laem Chabang Port, phase 3). The reclamation construction started in May 2021 and is expected to be completed in 2025. Nevertheless, only marine-based physical and biological environmental mitigation measures are presented because of the page limit of the conference. The marine-based environmental impacts are mostly related to sediment dispersion and concentration of suspended solids. This article shows that the joint-venture contractor of the reclamation project realizes the necessity of caring for society and the environment.