The concept of international investment law evolved mainly for the purpose of giving protection to foreign investment. That is why only investors can bring a claim of breach of protection standards before the investment arbitral tribunal and the tribunal only follows the concerned International Investment Agreements (IIAs) to determine such breach. However, with the advent of the concept of sustainable development, nowadays, environmental protection of a host State has become a major concern in competition with the investment protection before the investor-state arbitral tribunal. States are now frequently claiming the prevalence of their regulatory power for environmental protection over investment protection. In some cases, for example Glamis v US, the tribunal’s decision was influenced by the State’s regulatory power for environmental protection. In some recent cases, for example Burlington v Ecuador and Perenco v Ecuador, environmental issues arose with some separate standing. In these cases, the tribunals entertained host States’ counterclaims and awarded compensation against the investors. In such backdrop, I would like to have a detour in an arbitral decision wherein environmental issues were raised by the State for the first time. I want to look back how the tribunal had decided that case.