Obstacles to cross-border tourism cooperation across the Baltic Sea as seen by Interreg stakeholdersCross-border tourism cooperation offers significant benefits, yet it faces numerous barriers and obstacles. Unfortunately, studies on cross-border cooperation across sea borders remain limited, with a lack of scientific discourse on key topics such as obstacles to cooperation. To address this gap, this paper aims to identify and discuss the main obstacles to cross-border tourism cooperation across sea borders in the Baltic Sea region. Through qualitative analysis involving 35 in-depth interviews with stakeholders representing various aspects of tourism cooperation within the EU Interreg programme and different parts of the region, 43 distinct obstacles were identified. Among these, five obstacles were consistently mentioned by a significant portion of respondents: language barriers, poor human resources, reimbursement principles of financing projects, bureaucracy, and cultural differences. The identified obstacles were categorized and discussed in relation to the existing literature on cross-border cooperation barriers. Surprisingly, the Baltic Sea itself, often perceived as a hindrance due to vast distances and limited accessibility, was not highly ranked as an obstacle by stakeholders. Instead, it was seen as both a reason and an opportunity for cooperation. The research confirmed that the most significant obstacles to tourism cross-border cooperation in the Baltic Sea region align with those found in the literature on land borders, albeit with different importance.