Investment treaty arbitration has become a laboratory for testing the limits of international corporate responsibility, because arbitrators are often asked to consider instances of investors’ misconduct that compromise fundamental social values and interests. The decision in David Aven v Costa Rica is a glaring example of this case law. The dispute originated from a real estate project halted by local authorities for adversely impacting fragile ecosystems. This case note examines the arbitral tribunal’s approach to environmental harm caused by foreign investors.