This paper focuses on the changing role of energy and environment in Turkish-Bulgarian relations since the second half of the 2010s. The energy ties between the two countries strengthened since then after reaching at least two critical milestones. The first is the synchronous integration of Turkey's electricity grid to the EU power transmission network, and the second is the TurkStream natural gas pipeline that extends towards Bulgaria. These two crucial developments necessitated Turkey's energy laws to be in harmony with the EU regulations. On the other hand, Turkey's environmental policies are not fully harmonious with the EU policies and rules, and bilateral environmental relations remain relatively immature. This paper aims to analyze the main aspects of the energy, environment, and water policies in Turkish-Bulgarian relations and identify reasons for the challenges in the issue areas in the regional environment. The main research question of the paper is whether the main weaknesses in the implementation of environmental sustainability policies are related to governance issues in the countries. To answer this question, this paper compares the three aspects of Turkey's energy and environment relations with Bulgaria, i.e., natural gas trade, electricity trade, transboundary rivers. The methods used include examining fundamental laws, regulations, documents, and reports of the energy and environment regulators. The authors investigate the perceptions and opinions of the people, politicians, media, civil society, and political parties about energy trade and transboundary water issues. The paper argues that joint transboundary initiatives, strong incentives for cooperation, and the existing regulations in place since the early 2010s are insufficient to successfully implement environmental policies. Instead, government effectiveness is crucial for achieving a sustainable regional environment.